The PLC series pumps serve as the foundation for the development of the PLCF series pumps. This long-shaft submerged pump (also known as an absorption tower sump pump) is specially designed for underground tank stations in power plant flue gas desulfurization systems.Its submerged depth ranges from 3 to 6 meters. It is suitable for conveying media containing suspended particles, corrosive and abrasive fluids, viscous liquids, scaling liquids, and gas-containing liquids.Featuring advanced design, high overall unit reliability and long service life, the PLCF pump has been widely applied in the field of power plant flue gas desulfurization.
Structural Characteristics of PLCF Desulfurization Submerged Pump
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Adopts a sectional structure with rigid shafts for each section. Bearings are equipped with dust covers on both sides, requiring no grease lubrication. The forced lubrication device ensures a long service life of the seal.
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The impeller is a closed wide-flow design, which facilitates the passage of solid-containing media and prevents clogging. It is provided with front and rear back blades. The front blades block medium backflow toward the pump inlet, while the rear blades balance axial force and reduce axial leakage pressure, so as to improve pump efficiency.
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The shaft seal adopts a cartridge double mechanical seal structure, ensuring long-term stable submerged operation of the pump.
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Equipped with an intelligent monitoring and protection device, it prevents working liquid leakage and optimizes the external operating environment of the seal. It solves the technical problem of bearing damage caused by mechanical seal failure, and improves the overall reliability and service life of the pump. This device features ingenious design, simple structure, easy manufacturing and excellent performance.
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The shaft adopts large diameter and fewer shaft shoulders, delivering excellent rigidity.
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The support pipe and bearing housing are designed with high rigidity, ensuring stable pump operation.
Model Definition
Example：PLCF65-310
PLCF：Wear-resistant and corrosion-resistant long-shaft submerged pump
65：Discharge port diameter
310：Impeller outer diameter
Structural Analysis of Submerged Desulfurization Pumps
At present, submerged pumps used in desulfurization systems are divided into two structural types: non-seal structure and mechanical seal structure.
1. Non-seal Structure
As shown in Figure 1, there is no sealing element between the impeller hub and the rear cover plate, with a large clearance reserved. This structure is commonly applied to ordinary slurry submerged pumps, with the slurry tank depth generally not exceeding 2.5 m, and it is rarely used in desulfurization submerged pumps.
When adopted for long-shaft submerged pumps in desulfurization systems, this structure has two prominent problems. First, the long impeller cantilever produces large deflection under centrifugal force during operation, causing pump vibration and even abnormal operation. Second, without shaft sealing, the pump shaft runs at high speed in corrosive media, which imposes high requirements on the corrosion resistance of shaft materials.
2. Mechanical Seal Structure
Most long-shaft submerged pumps for desulfurization systems adopt mechanical seals, as shown in Figure 2.The high-speed underwater rotation of the vertical pump impeller generates huge radial force, resulting in excessive shaft deflection at the mechanical seal mounting position. This causes uneven stress on sealing faces and poor sealing performance.
Therefore, supports are installed above the mechanical seal to shorten the cantilever length, and rolling bearings are widely used for auxiliary support. Meanwhile, the mechanical seal can effectively isolate the slurry from the pump shaft. Conventional materials can be used for the shaft instead of expensive corrosion-resistant materials, which reduces manufacturing costs.
Key Points of Shaft Seal Structure for Long‑Shaft Submerged Pumps in Desulfurization Systems
In desulfurization systems, mechanical seals shall be adopted for the shaft seals of long‑shaft submerged pumps. Due to the special working conditions of long‑shaft submerged pumps, the requirements for mechanical seals differ from those for ordinary models.
To ensure wear and erosion resistance of friction pairs in particle‑containing media, the hardness of friction pair materials must be higher than that of abrasive particles. A hard‑to‑hard mating combination is generally recommended, with optional materials such as tungsten carbide and silicon carbide. Compared with tungsten carbide, silicon carbide features higher hardness, superior thermal conductivity, excellent chemical stability and self‑lubricating property, though at a higher cost. Meanwhile, the width of the friction pair shall be greater than that of mechanical seals for clean water pumps, and the friction pair shall be designed with sharp edges to prevent solid particles from entering the sealing faces as much as possible. The spring adopts a stationary type with compensation realized through the stationary ring. Installed inside the gland and isolated from solid particles, the spring effectively reduces wear and prevents failure caused by blockage, ensuring flexible, stable and reliable compensation performance.
Since the slurry contains a large number of solid particles, the seal chamber is designed as an open structure to prevent particle deposition around the friction pair after pump shutdown, which would affect subsequent startup. This design also enables flushing water in the desulfurization system to discharge particulate residues inside the seal chamber.
The seal chamber is structurally optimized to realize complete gas venting and avoid dry friction of the mechanical seal. Vent holes are drilled on the rear pump casing for gas discharge.
The structural type of the mechanical seal shall be selected according to the solid content of the slurry. For low‑solid slurry, a single‑end mechanical seal is applied, relying on the medium itself for cooling and lubrication. The structural design shall minimize particle accumulation around the friction pair. For high‑solid slurry, the lubricating performance of the medium declines with increased particle content. Accordingly, a double‑end mechanical seal is adopted, with external seal water provided for cooling, lubrication and leakage blocking.
Summary of Desulfurization Long-shaft Submerged Pumps
All long-shaft submerged pumps in the desulfurization system adopt submerged bearing support to reduce impeller deflection and suppress vibration. For low-concentration slurry, single mechanical seals without flushing water are used; for high-concentration slurry, double mechanical seals with seal water are equipped. In addition, the structural design shall fully avoid sedimentation and deposition of medium around friction pairs, and take into account the gas venting requirement at the periphery of mechanical seal friction pairs.
