1 PLCFSubmerged desulfurization pumpbrief introduction

The PLCF series pump is a long axis submersible pump (also known as an absorption tower pit pump) designed and developed by the company for the underground tank station of power plant flue gas desulfurization based on the development of PLC series pumps. Its submersible depth is 3-6 meters, suitable for transporting liquids containing suspended particles, corrosive, abrasive media, viscous media, liquids with scaling characteristics, and liquids containing gases. The pump has advanced design, high overall reliability, and long service life, and has been widely used in the field of flue gas desulfurization in power plants. Its uniquely designed intelligent monitoring and protection device has obtained a national utility model patent.

2、 Structural characteristics of PLCF desulfurization submersible pump

(1) Adopting a segmented structure, with each segment being a rigid shaft; The bearing is equipped with dust covers on both sides and does not require lubricating grease; The forced lubrication device ensures the sealing service life.

(2) The impeller is a closed wide flow to the impeller, which is conducive to the passage of solid media without causing blockage. The impeller has front and rear back blades, with the front back blades used to prevent the medium from flowing back towards the pump inlet direction, and the back blades used to balance axial force and ground leakage pressure to improve pump efficiency;

(3) The shaft seal adopts a containerized double end mechanical seal structure to ensure that the pump runs smoothly underwater for a long time.

(4) The intelligent monitoring and protection device, which has obtained a national utility model patent, can prevent the leakage of working fluid, improve the external environment of sealed operation, overcome the technical problem of bearing damage caused by mechanical seal failure, and improve the reliability and service life of the entire pump. The device is ingeniously designed, structurally simple, easy to manufacture, and has good usability.

(5) The shaft diameter is thick, the shaft steps are few, and the rigidity of the shaft is good.

(6) The design of the support tube and bearing box has good rigidity, and the pump runs smoothly.

3、 The significance of the model of desulfurization submersible pump

Example: PLCF65-310

PLCF - Wear resistant and corrosion-resistant long shaft submersible pump

65- Discharge outlet diameter

310- Outer diameter of impeller

4、 Structural analysis of underwater desulfurization pump

At present, there are two types of submersible pump structures used in desulfurization systems, namely those without shaft seals and those with shaft seals (mechanical seals).

1) No shaft seal mechanism

As shown in Figure 1, there is no shaft seal between the impeller hub and the rear guard plate, leaving a large gap. This type of structure is commonly used in ordinary slag slurry pumps, and the depth of the slurry pool is mostly ≤ 2.5m. It is less commonly used in liquid pumps in desulfurization systems. There are two main issues with the application of this type of structure in the long axis submerged pump of desulfurization systems. One reason is that during pump operation, due to the long cantilever of the impeller, the deflection is large under the action of centrifugal force, which can cause pump vibration and even render it inoperable; Secondly, due to the lack of shaft seals, the pump shaft operates at high speeds in corrosive media, requiring high corrosion resistance of the pump shaft material.

2) Mechanical seal mechanism

Mechanical seals are commonly used for the shaft seals of long axis submersible pumps in desulfurization systems, as shown in Figure 2.

Due to the high-speed rotation of the vertical pump impeller underwater, a large radial force is generated. When the pump shaft is running, the deflection generated at the mechanical seal installation site is large, resulting in uneven force distribution between the sealing surfaces and poor sealing effect. Therefore, it is necessary to set up supports on the mechanical seal to reduce the length of the cantilever, and rolling bearings are often used for support. Simultaneously using mechanical seals can effectively prevent the slurry from coming into contact with the pump shaft. The shaft material can be made of ordinary materials, avoiding the use of corrosion-resistant materials and increasing costs.

5、 Key points of shaft seal structure for long axis submersible pump in desulfurization system

In the desulfurization system, mechanical seals should be used for the shaft seal of the long shaft submerged pump. Due to the special operating conditions of long axis submersible pumps, the requirements for mechanical seals are different from those for ordinary mechanical seals.

1) In order to ensure the wear resistance and corrosion resistance of the friction pair in the granular medium, the hardness of the friction pair material must be higher than that of the abrasive particles. Usually, hard to hard combinations can be used, and the material can be tungsten carbide or silicon carbide. Compared with tungsten carbide, silicon carbide has higher hardness, better thermal conductivity, better chemical stability, and self-lubricating properties, but the cost is higher. At the same time, the width of the friction pair should be wider than that of the mechanical seal used in the water pump, and the friction pair should have sharp edges to prevent solid particles from entering between the sealing surfaces as much as possible. The spring is a static type, compensated by a static ring. The spring is placed inside the cover and does not come into contact with solid particles, which can reduce wear and avoid failure caused by spring blockage, ensuring flexible, stable, and reliable compensation.

2) Due to the presence of a large number of medium particles in the slurry, in order to avoid the deposition of particles around the mechanical seal friction pair after pump shutdown, which may affect the next start and operation of the pump, the sealing chamber is designed to be open, which is also beneficial for the backwash water in the desulfurization system to take away the medium particles in the sealing chamber.

3) In the design of the sealed chamber structure, it should be ensured that the gas inside the sealed chamber can be evacuated to avoid dry friction of the mechanical seal. An exhaust hole should be drilled on the rear pump casing.

4) The structural form of mechanical seals varies depending on the solid content of the slurry. When the solid content of the slurry is low, a single end mechanical seal is used, and the mechanical seal is cooled and lubricated by the medium itself. However, attention should be paid to the structural design of the mechanical seal to avoid the accumulation of medium particles around the friction pair as much as possible. When the solid content of the slurry is high, the lubrication effect of the medium deteriorates due to the increase of particles. Therefore, a double end mechanical seal is used, which is cooled, lubricated, and sealed by external shaft seal water.

6、 Summary of desulfurization submersible pump

In the long axis submersible pump of the desulfurization system, all are supported by submersible bearings to reduce impeller deflection and avoid vibration. When the slurry concentration is low, a single end mechanical seal without flushing water is used; When the slurry concentration is high, a mechanical seal with double end face and shaft seal water is used. At the same time, in the structural design, it is necessary to fully consider factors such as avoiding the precipitation and sedimentation of the medium around the friction pair, as well as the exhaust of gas around the mechanical seal friction pair.