A lubricating oil production wastewater treatment device

Abstract

This invention relates to a wastewater treatment device for lubricating oil production, comprising a pretreatment device, a filter, and a biochemical treatment device including a neutralization tank and a flow pipe, with an avoidance groove on an adjusting rod; it also includes a rotating cylinder, a liquid distribution pipe, and a connecting pipe, with a limiting groove on the connecting pipe; a counterweight is fixedly connected to the bottom of the rotating cylinder, and one end of the liquid distribution pipe is inserted into the rotating cylinder and presses against the limiting groove; a rotating rod is rotatably connected to the middle of the neutralization tank, which is movable and passes through the connecting pipe, and a stirring plate is provided at the bottom of the rotating rod that presses against the counterweight; this application extends the wastewater path by setting a spiral flow pipe, and achieves preliminary diversion of wastewater with the avoidance groove on the adjusting rod; by utilizing the cooperative structure of the rotating cylinder, counterweight, and liquid distribution pipe, the wastewater can enter the bottom of the neutralization tank at multiple angles and dynamically after being pressed against the counterweight by the stirring plate, while the rotating rod drives the stirring plate to rotate, significantly improving the mixing uniformity of wastewater and chemical solution and the neutralization reaction efficiency.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a wastewater treatment device for lubricating oil production. Background Technology

[0002] The production of lubricating oil generates a large amount of complex wastewater containing recalcitrant organic matter and emulsified oil. This wastewater requires pretreatment, biochemical treatment, and deep filtration before discharge or reuse. Biochemical treatment typically involves adding neutralizing agents to the wastewater in a neutralization tank to adjust the pH value and create suitable conditions for subsequent biological treatment. However, in existing neutralization methods, insufficient uniformity of mixing between wastewater and the agent is a significant technical problem. In traditional structures, the agent and wastewater do not come into sufficient contact within the neutralization tank, leading to incomplete neutralization and large pH fluctuations. This not only affects the neutralization effect itself but also negatively impacts the stable operation of subsequent biological treatment units.

[0003] Therefore, a wastewater treatment device for lubricating oil production is proposed to address the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a wastewater treatment device for lubricating oil production.

[0005] The objective of this invention is achieved through the following technical solution: a lubricating oil production wastewater treatment device, comprising: a pretreatment device, wherein the wastewater enters sequentially through the pretreatment device into a biochemical treatment device and a filter containing an activated carbon layer, the biochemical treatment device comprising a neutralization tank, the neutralization tank being connected to a dosing system, a spiral-shaped flow pipe being fixedly connected to the inner wall of the neutralization tank, an adjusting rod being movably inserted into the flow pipe, and an avoidance groove being provided on the adjusting rod; It also includes a rotating cylinder and a liquid distribution pipe fixed to the rotating cylinder. A connecting pipe is fixedly connected to the bottom of the flow pipe. A limit groove is opened on the connecting pipe. The rotating cylinder is movably sleeved on the connecting pipe and corresponds to the position of the limit groove. A counterweight is fixedly connected to the bottom of the rotating cylinder. One end of the liquid distribution pipe is located inside the rotating cylinder and is in abutting fit with the limit groove. A rotating rod with a movable through-connecting pipe is rotatably connected to the middle of the neutralization tank. The bottom of the rotating rod is equipped with a stirring plate that presses against the counterweight. The wastewater path is extended by setting a spiral flow pipe, and the wastewater is initially diverted by adjusting the clearance groove on the plug rod. The cooperative structure of the rotating cylinder, counterweight, and liquid distribution pipe allows the wastewater to enter the bottom of the neutralization tank at multiple angles and dynamically after being pressed against the counterweight by the stirring plate. At the same time, the rotating rod drives the stirring plate to rotate, which significantly improves the mixing uniformity of wastewater and chemical solution and the neutralization reaction efficiency.

[0006] As a further description of the above technical solution: An electric telescopic rod is fixedly connected to the outer surface of the neutralization tank, and the telescopic end of the electric telescopic rod is connected and fixed to the adjusting rod. The movement of the adjusting rod is precisely controlled by the electric telescopic rod, thereby realizing the automatic adjustment of the opening size of the avoidance tank, and thus flexibly controlling the amount of wastewater directly entering the neutralization tank, making the liquid inlet method controllable and easy to adapt to the treatment needs under different working conditions.

[0007] As a further description of the above technical solution: A sealing sleeve is fixedly connected to the outer surface of the neutralization tank. The telescopic end of the electric telescopic rod and the adjusting rod have the same diameter and both move within the sealing sleeve. By setting the sealing sleeve and ensuring that the telescopic end of the electric telescopic rod and the adjusting rod have the same diameter and both move within it, the sealing of the moving part of the adjusting rod is effectively guaranteed, preventing liquid leakage from the neutralization tank or intrusion of external impurities, and improving the safety and stability of equipment operation.

[0008] As a further description of the above technical solution: The connecting pipe is fixedly connected with limiting rings located on both sides of the limiting groove. The limiting rings are located at both ends of the rotating cylinder. By setting limiting rings on both sides of the limiting groove and limiting the rotating cylinder between the two limiting rings, the rotating cylinder is effectively prevented from moving along the axial direction of the connecting pipe. This ensures that the rotating cylinder can only make a stable circumferential rotation around the connecting pipe, and ensures that the liquid distribution pipe and the limiting groove always maintain a precise fit.

[0009] As a further description of the above technical solution: The rotating cylinder is also provided with water passage holes on both sides of the liquid distribution pipe, which is a lightweight pipe. The water passage holes increase the flow channel for wastewater to enter the tank. The lightweight liquid distribution pipe is lightweight and sensitive to movement. With the help of the counterweight, it can achieve a more flexible swing response, allowing wastewater to enter the tank in a multi-directional spray manner, further improving the uniformity of wastewater dispersion in the tank.

[0010] As a further description of the above technical solution: A motor is fixedly connected to the top of the neutralization tank. The motor output shaft is fixedly connected to a rotating rod. Multiple mating plates are fixedly connected to the rotating rod. The mating plates and stirring plates are inclined. The motor provides stable power to the rotating rod. The inclined mating plates and stirring plates generate greater turbulence when rotating, which effectively enhances the stirring intensity of the liquid in the tank. At the same time, the stirring plates periodically press against the counterweight, providing a reliable driving force for the reciprocating oscillation of the rotating cylinder.

[0011] As a further description of the above technical solution: A flow guide groove is provided on one side of the outer surface of the rotating rod. The bottom end of the flow guide groove is located inside the connecting pipe, and the top end of the flow guide groove is located outside the connecting pipe. By providing a flow guide groove on one side of the rotating rod, with the bottom end inside the connecting pipe and the top end outside the connecting pipe, some of the wastewater inside the connecting pipe can be discharged from the middle or upper part of the tank, achieving the distribution of wastewater at different height levels and avoiding excessively high local concentrations caused by wastewater entering only from the bottom.

[0012] As a further description of the above technical solution: A U-shaped hole is provided on the other side of the outer surface of the rotating rod. The bottom end of the U-shaped hole is located inside the connecting pipe, and the top end of the U-shaped hole is located outside the connecting pipe. A mating hole communicating with the U-shaped hole is also provided on the rotating rod. The combination of the U-shaped hole and the mating hole provides another independent wastewater discharge path, allowing wastewater to enter the neutralization tank from more different heights and angles, thereby achieving a wider and more uniform contact with the liquid medicine and enhancing the three-dimensional mixing effect.

[0013] As a further description of the above technical solution: The top of the flow pipe is fixedly connected to an inlet pipe that extends out of the neutralization tank. The inlet pipe is connected to the pretreatment device, and the neutralization tank is also connected to an outlet pipe that is connected to the filter. The inlet pipe ensures that the pretreated wastewater enters the flow pipe smoothly, while the outlet pipe stably guides the neutralized wastewater to the filter.

[0014] As a further description of the above technical solution: The rotating cylinder is equipped with a U-shaped rod, with both ends of the U-shaped rod inserted into the liquid distribution pipe. The diameter of both ends of the U-shaped rod is smaller than the diameter of the liquid distribution pipe. The U-shaped rod, with both ends inserted into the liquid distribution pipe and having a smaller diameter than the liquid distribution pipe, plays a guiding and limiting role during the reciprocating swing and reset process of the rotating cylinder. It provides a certain swing margin for the liquid distribution pipe and assists the counterweight to achieve reliable reset, ensuring the periodicity and stability of the operation of the rotating cylinder and the liquid distribution pipe.

[0015] Compared with the prior art, the advantages of the present invention are as follows: This application relates to a unique inlet and mixing structure of the neutralization tank in a biochemical treatment device. After pretreatment, wastewater enters the neutralization tank through a spiral flow pipe. During operation, a motor-driven rotor continuously rotates an agitator plate, which periodically presses against a counterweight, causing the rotating cylinder to reciprocate around the connecting pipe at a certain angle. This causes the distribution pipe and water passage holes to oscillate accordingly, allowing wastewater to enter the bottom of the neutralization tank dynamically from multiple angles. Simultaneously, during the rotor's rotation, some wastewater enters from different heights within the tank through its guide channels and U-shaped holes. This synergistic effect of a small amount of wastewater entering from multiple points and heights, while the majority enters dynamically from the bottom, ensures thorough and uniform mixing of the wastewater with the chemical solution within the tank, effectively improving the efficiency and effectiveness of the neutralization reaction. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a cross-sectional structural diagram of the neutralization tank of the present invention; Figure 3 This is the present invention. Figure 2 Enlarged structural diagram of area A in the middle; Figure 4 This is a schematic diagram showing the disassembled structure of the neutralization tank and the flow pipe of the present invention; Figure 5 This is a schematic diagram showing the disassembled structure of the flow tube and the adjusting rod of the present invention; Figure 6 This is a schematic diagram of the cross-sectional structure of the flow tube of the present invention; Figure 7 This is a schematic diagram showing the disassembled structure of the flow tube and connecting tube of the present invention; Figure 8 This is a schematic diagram of the disassembled structure of the connecting pipe and the rotating cylinder of the present invention; Figure 9 This is a schematic diagram of the cooperation structure between the stirring plate and the counterweight block of the present invention; Figure 10 This is a cross-sectional structural diagram of the connecting pipe and rotating cylinder of the present invention; Figure 11 This is a cross-sectional structural diagram of the rotating rod of the present invention.

[0017] Labeling Explanation: 1. Neutralization Tank; 2. Dosing System; 3. Flow Pipe; 4. Adjusting Rod; 5. Clearance Groove; 6. Rotating Cylinder; 7. Distribution Pipe; 8. Connecting Pipe; 9. Limiting Groove; 10. Counterweight; 11. Rotating Rod; 12. Stirring Plate; 13. Electric Telescopic Rod; 14. Sealing Sleeve; 15. Limiting Ring; 16. Water Passage Hole; 17. Motor; 18. Mating Plate; 19. Guide Groove; 20. U-shaped Hole; 21. Mating Hole; 22. Inlet Pipe; 23. Outlet Pipe; 24. U-shaped Rod. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and embodiments: like Figures 1-11 The diagram shows an embodiment of a lubricating oil production wastewater treatment device provided by the present invention, including: a pretreatment device, through which wastewater sequentially enters a biochemical treatment device and a filter containing an activated carbon layer; the biochemical treatment device includes a neutralization tank 1, which is connected to a dosing system 2; a spiral-shaped flow pipe 3 is fixedly connected to the inner wall of the neutralization tank 1; an adjusting rod 4 is movably inserted into the flow pipe 3; and an avoidance groove 5 is provided on the adjusting rod 4. It also includes a rotating cylinder 6 and a liquid distribution pipe 7 that is connected and fixed to the rotating cylinder 6. A connecting pipe 8 is fixedly connected to the bottom of the flow pipe 3. A limiting groove 9 is opened on the connecting pipe 8. The rotating cylinder 6 is movably sleeved on the connecting pipe 8 and corresponds to the position of the limiting groove 9. A counterweight block 10 is fixedly connected to the bottom of the rotating cylinder 6. One end of the liquid distribution pipe 7 is located inside the rotating cylinder 6 and is in abutting fit with the limiting groove 9. A rotating rod 11, which is rotatably connected to a movable through-connecting pipe 8, is located in the middle of the neutralization tank 1. At the bottom of the rotating rod 11 is a stirring plate 12 that presses against the counterweight 10. After pretreatment, the wastewater enters the spiral flow pipe 3. Adjusting the insertion rod 4 changes the opening of the clearance groove 5, allowing some wastewater to directly enter the tank. Most of the wastewater enters the rotating cylinder 6 through the connecting pipe 8 and is discharged through the distribution pipe 7. The rotating rod 11 drives the stirring plate 12 to rotate, periodically pressing against the counterweight 10, causing the rotating cylinder 6 to oscillate back and forth around the connecting pipe 8, thus enabling the wastewater to dynamically enter the bottom of the tank from multiple angles.

[0019] An electric telescopic rod 13 is fixedly connected to the outer surface of the neutralization tank 1. The telescopic end of the electric telescopic rod 13 is connected and fixed to the adjusting rod 4. After receiving the control signal, the electric telescopic rod 13 extends and retracts precisely, driving the adjusting rod 4 to move along the direction of the flow pipe 3, thereby adjusting the exposure area of ​​the avoidance groove 5 inside and outside the flow pipe 3, so as to control the amount of wastewater flowing directly into the tank from the avoidance groove 5.

[0020] A sealing sleeve 14 is fixedly connected to the outer surface of the neutralization tank 1. The telescopic end of the electric telescopic rod 13 and the adjusting rod 4 have the same diameter and both move within the sealing sleeve 14. The telescopic end and the adjusting rod 4 are coaxial and have the same diameter. They slide within the sealing sleeve 14, forming a dynamic seal using the inner wall of the sleeve, which effectively prevents the liquid in the tank from leaking out along the gap of the adjusting rod 4.

[0021] Limiting rings 15 are fixedly connected to the connecting pipe 8 on both sides of the limiting groove 9. The limiting rings 15 are located at both ends of the rotating cylinder 6. The two limiting rings 15 clamp the rotating cylinder 6 in the middle, restricting the rotation of the rotating cylinder 6 along the axial direction of the connecting pipe 8.

[0022] The rotating cylinder 6 is also provided with water passage holes 16 located on both sides of the liquid distribution pipe 7. The liquid distribution pipe 7 is a lightweight pipe. The water passage holes 16 serve as additional water outlet channels, increasing the wastewater discharge points. The lightweight pipe has a small mass and low motion inertia, which makes the rotating cylinder 6 swing more flexibly and respond more quickly under the action of the counterweight 10 and the stirring plate 12.

[0023] A motor 17 is fixedly connected to the top of the neutralization tank 1. The output shaft of the motor 17 is fixedly connected to the rotating rod 11. Multiple mating plates 18 are fixedly connected to the rotating rod 11. The mating plates 18 and the stirring plates 12 are inclined. The motor 17 drives the rotating rod 11 to rotate, which in turn drives the mating plates 18 and the stirring plates 12 to rotate synchronously and slowly. The inclined plates generate greater axial and radial turbulence when stirring the liquid, which enhances the stirring effect. At the same time, the stirring plates 12 continuously strike the counterweight 10 during rotation.

[0024] A guide groove 19 is provided on one side of the outer surface of the rotating rod 11. The bottom end of the guide groove 19 is located inside the connecting pipe 8, and the top end of the guide groove 19 is located outside the connecting pipe 8. Some of the wastewater in the connecting pipe 8 enters the bottom end of the guide groove 19 under pressure, rotates with the rotating rod 11, and is discharged from the top end located outside the connecting pipe 8, thereby introducing the wastewater into the middle or upper area of ​​the neutralization tank 1.

[0025] A U-shaped hole 20 is provided on the other side of the outer surface of the rotating rod 11. The bottom end of the U-shaped hole 20 is located inside the connecting pipe 8, and the top end of the U-shaped hole 20 is located outside the connecting pipe 8. A mating hole 21 communicating with the U-shaped hole 20 is also provided on the rotating rod 11. Another part of the wastewater in the connecting pipe 8 flows in through the bottom end of the U-shaped hole 20 and is discharged from the top to a higher position in the tank. At the same time, the mating hole 21 further increases the water outlet path, thereby working in conjunction with the guide channel 19 to achieve multi-point water distribution of wastewater at different heights in the tank.

[0026] The top of the flow pipe 3 is fixedly connected to the inlet pipe 22 that extends out of the neutralization tank 1. The inlet pipe 22 is connected to the pretreatment device. The neutralization tank 1 is also connected to the outlet pipe 23 that is connected to the filter. The inlet pipe 22 introduces the pretreated wastewater into the flow pipe 3, and the outlet pipe 23 discharges the neutralized mixture to the filter for further treatment, forming a complete continuous water treatment circuit.

[0027] The rotating cylinder 6 is equipped with a U-shaped rod 24, with both ends of the U-shaped rod 24 inserted into the liquid distribution pipe 7. The diameter of both ends of the U-shaped rod 24 is smaller than the diameter of the liquid distribution pipe 7. The U-shaped rod 24 provides support and guidance for the liquid distribution pipe 7, allowing the liquid distribution pipe 7 to have a certain amount of movement when the rotating cylinder 6 swings. When the stirring plate 12 is disengaged from the counterweight 10, the U-shaped rod 24, in conjunction with the gravity of the counterweight 10, assists the rotating cylinder 6 and the liquid distribution pipe 7 to quickly and stably return to their initial positions, ensuring the periodicity of the swing.

[0028] Working principle: After the pretreatment device removes floating oil, emulsified oil and suspended solids from the wastewater, the treated wastewater enters the flow pipe 3 through the inlet pipe 22 and then enters the neutralization tank 1. At the same time, the dosing system 2 continuously adds neutralizing solution, and the wastewater and the neutralizing solution in the neutralization tank 1 are uniformly mixed. There are multiple pathways through which flow pipe 3 enters neutralization tank 1, as detailed below: First, the electric telescopic rod 13 drives the adjusting rod 4 to move, thereby moving the clearance trough 5 which is completely located inside the flow pipe 3. Half of the clearance trough 5 is located inside the flow pipe 3, and the other half of the clearance trough 5 is located outside the flow pipe 3, so that a small part of the wastewater in the flow pipe 3 enters the neutralization tank 1 through the clearance trough 5 and mixes with the neutralization solution.

[0029] Second, the wastewater passes through the flow pipe 3 and enters the connecting pipe 8, and then enters the neutralization tank 1 through the liquid distribution pipe 7 and the water passage hole 16. It is worth noting that: while the motor 17 drives the rotating rod 11 to rotate, it also drives the stirring plate 12 to make a circular motion. The stirring plate 12 rotates and contacts the counterweight 10, thereby pressing against the counterweight 10 and causing the counterweight 10 to make a circular motion at a certain angle. At the same time, the rotating cylinder 6 rotates around the connecting pipe 8 as the axis of rotation, thereby changing the position of the liquid distribution pipe 7 and the water passage hole 16. When the counterweight 10 is separated from the continuously rotating stirring plate 12, the rotating cylinder 6 is reset under the action of the counterweight 10 and the U-shaped rod 24. This process causes the liquid distribution pipe 7 and the water passage hole 16 to reciprocate at a certain angle, so that most of the wastewater enters the bottom of the neutralization tank 1 from multiple angles. One end of the liquid distribution pipe 7 is located inside the rotating cylinder 6, and the liquid distribution pipe 7 will not rotate excessively under the restriction of the limiting groove 9.

[0030] Third, during the rotation of the rotating rod 11, a small amount of wastewater enters the guide channel 19 and U-shaped hole 20 from the connecting pipe 8, and enters the neutralization tank 1 from the other end of the guide channel 19, the other end of the U-shaped hole 20, and the mating hole 21.

[0031] This application achieves a uniform neutralization reaction by introducing a small amount of wastewater into different heights within the neutralization tank 1, while the majority of the wastewater enters from the bottom of the neutralization tank 1.

[0032] Specifically, in the description of this specification, the references to terms such as "an embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to well understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A wastewater treatment device for lubricating oil production, comprising: The pretreatment device allows wastewater to enter the biochemical treatment device and the filter containing the activated carbon layer in sequence. The biochemical treatment device includes a neutralization tank (1), which is connected to a dosing system (2). A spiral-shaped flow pipe (3) is fixedly connected to the inner wall of the neutralization tank (1). An adjusting rod (4) is movably inserted into the flow pipe (3), and a clearance groove (5) is provided on the adjusting rod (4). It also includes a rotating cylinder (6) and a liquid distribution pipe (7) that is fixed to the rotating cylinder (6). The bottom of the flow pipe (3) is fixedly connected to a connecting pipe (8). A limiting groove (9) is opened on the connecting pipe (8). The rotating cylinder (6) is movably sleeved on the connecting pipe and corresponds to the position of the limiting groove (9). A counterweight (10) is fixedly connected to the bottom of the rotating cylinder (6). One end of the liquid distribution pipe (7) is inserted into the rotating cylinder (6) and presses against the limiting groove (9). The neutralization tank (1) has a rotating rod (11) with a movable through connecting pipe in the middle. The bottom of the rotating rod (11) is provided with a stirring plate (12) that presses against the counterweight (10).

2. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: An electric telescopic rod (13) is fixedly connected to the outer surface of the neutralization tank (1), and the telescopic end of the electric telescopic rod (13) is connected and fixed to the adjusting rod (4).

3. The lubricating oil production wastewater treatment equipment according to claim 2, characterized in that: The neutralization tank (1) is fixedly connected to a sealing sleeve (14) on its outer surface. The telescopic end of the electric telescopic rod (13) and the adjusting rod (4) have the same diameter and both move within the sealing sleeve (14).

4. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: The connecting pipe (8) is fixedly connected with limiting rings (15) located on both sides of the limiting groove (9), and the limiting rings (15) are located at both ends of the rotating cylinder (6).

5. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: The rotating cylinder (6) is also provided with water passage holes (16) located on both sides of the liquid distribution pipe (7), and the liquid distribution pipe (7) is a lightweight pipe.

6. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: The neutralization tank (1) is fixedly connected to a motor (17) at the top. The output shaft of the motor (17) is fixedly connected to a rotating rod (11). Multiple mating plates (18) are fixedly connected to the rotating rod (11). The mating plates (18) and the stirring plate (12) are distributed at an inclination.

7. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: A guide groove (19) is provided on one side of the outer surface of the rotating rod (11). The bottom end of the guide groove (19) is located inside the connecting pipe (8), and the top end of the guide groove (19) is located outside the connecting pipe (8).

8. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: A U-shaped hole (20) is provided on the other side of the outer surface of the rotating rod (11). The bottom end of the U-shaped hole (20) is located inside the connecting pipe (8), and the top end of the U-shaped hole (20) is located outside the connecting pipe (8). A mating hole (21) communicating with the U-shaped hole (20) is also provided on the rotating rod (11).

9. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: The top end of the flow pipe (3) is fixedly connected to an inlet pipe (22) that extends out of the neutralization tank (1). The inlet pipe (22) is connected to the pretreatment device. The neutralization tank (1) is also connected to an outlet pipe (23) that is connected to the filter.

10. The lubricating oil production wastewater treatment equipment according to claim 1, characterized in that: The rotating cylinder (6) is equipped with a U-shaped rod (24), with both ends of the U-shaped rod (24) inserted into the liquid distribution pipe (7). The diameter of both ends of the U-shaped rod (24) is smaller than the diameter of the liquid distribution pipe (7).

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