FGD Pumps

Types of FGD Pumps

Key Functions of FGD Pumps

Absorber Recirculation: The most vital function; these pumps continuously circulate limestone or lime slurry to the top of the spray tower. This ensures a dense mist that reacts with upward-moving flue gas to neutralize pollutants.
Slurry Transportation: They move abrasive and corrosive gypsum slurries from the absorption tank to dewatering systems, facilitating the creation of usable byproducts.
Reaction Maintenance: By controlling flow rates, FGD pumps maintain the chemical equilibrium and temperature within the tower, ensuring maximum SO₂ removal efficiency.
System Protection: Engineered with duplex stainless steel or specialized rubber linings, these pumps are built to survive the high-chloride, low-pH environments that would destroy standard equipment.

FGD Pumps' Key Design Features

Back Pull-Out Structure: This allows maintenance crews to remove the rotating assembly without disconnecting the suction or discharge piping, significantly reducing downtime.
Large Diameter, Slow-Speed Impellers: To minimize erosion, FGD pumps utilize large impellers that move vast volumes of slurry at lower RPMs. This reduced velocity extends the lifespan of internal components.
Advanced Metallurgy: Wetted parts are often cast from A49 or natural rubber linings, providing the high-hardness needed for abrasive gypsum and the acid resistance required for low pH environments.
Specialized Slurry Seals: Integrated mechanical seals, often utilizing silicon carbide faces, operate without external flush water to prevent dilution of the absorber slurry while keeping abrasive particles out of the motor.

How to Select Pumps Suitable for Desulfurization and Denitrification Processes?

Selecting appropriate pumps for desulfurization and denitrification processes demands comprehensive consideration of multiple key factors, as detailed below:

Medium Characteristics: The slurry involved in these processes is highly corrosive and has high solid content. Acidic components like sulfuric acid can erode pump bodies, so corrosion-resistant materials such as stainless steel or fluoroplastic are preferred. For slurries containing solid particles (e.g., limestone, gypsum), wear-resistant pumps (e.g., slurry pumps) with impellers and casings made of wear-resistant materials are essential to mitigate particle erosion.
Process Parameters: Accurate calculation of flow rate and head is critical. Determine flow rate based on system processing scale—high-flow pumps are usually required for desulfurization tower circulation. Calculate head by considering slurry transportation height and system resistance, ensuring the pump’s rated parameters meet maximum system requirements with a 10%–20% margin. Additionally, match pressure capabilities to process needs, such as high-pressure pumps for denitrification injectors to ensure effective reductant injection.
Operating Conditions: Prioritize reliability and stability for continuous long-term operation; select mature, reputable models and equip backup pumps. For high ambient temperatures (e.g., summer or near high-temperature equipment), choose high-temperature-adaptable pumps or install cooling measures to avoid component damage.
Maintenance and Cost: Opt for simple structures to facilitate daily maintenance. Evaluate total lifecycle costs rather than just initial investment—high-efficiency, reliable pumps may have higher upfront costs but save energy and reduce repair expenses long-term.
Safety Performance: For flammable/explosive media (e.g., liquid ammonia in denitrification), explosion-proof pumps are mandatory to ensure operational safety.

Operation Principle and Maintenance of Desulfurization Slurry Recirculation Pumps

As the core equipment in desulfurization systems, desulfurization slurry recirculation pumps adopt an efficient centrifugal design, responsible for extracting and recirculating slurry from the absorption tower bottom. Among all pumps in the limestone-gypsum flue gas desulfurization process, they handle the largest flow rate and operate under the harshest conditions. Long-term exposure to corrosion and abrasion leads to frequent failures, making their operation and maintenance particularly critical.

Characteristics of the Operating Medium

► Abrasiveness: The slurry contains solid particles (fly ash, CaSO₃·½H₂O, CaSO₄·2H₂O) with a particle size range of 0-400 μm (over 90% between 20-60 μm) and a mass concentration of 5%-28%, causing severe pump wear.

► Corrosiveness: The tower bottom slurry maintains an acidic pH of 4-6. When Cl⁻ concentration exceeds 20,000 mg/L, the corrosiveness intensifies, severely damaging system equipment and pipelines.

► Cavitation and Gas Entrainment: Entrained gas during slurry transport reduces pump flow, head, and efficiency. With gas content increasing, noise and vibration escalate, damaging the shaft, bearings, and seals. Pump performance deteriorates sharply when gas content (by volume) reaches ~3%.

Piping Design and Operation

► Inlet and Outlet Design: The inlet pipeline is equipped with strainers, motorized valves, flow meters, rubber flexible connectors, and vent valves to ensure smooth suction. The outlet is fitted with rubber flexible connectors, pressure gauges, and backflush motorized butterfly valves. Large pumps usually have no standby units or outlet valves, requiring reverse rotation resistance design.

► Inspection and Maintenance: Temporary inflatable bags are used during maintenance to prevent flue gas backflow. Motorized butterfly valves have butyl rubber linings and Hastelloy alloy discs/shafts. Rubber flexible connectors compensate for thermal expansion stress and prevent vibration transmission.

► Strainers and Flushing: Inlet strainers (stainless steel, 5-25 mm holes, 2-3 times the inlet pipe flow area) prevent large gypsum particles from damaging the pump or clogging nozzles. Flushing lines are required for startup/shutdown; the pipeline and pump casing are emptied via drain valves. The pump should be filled with clean water and the inlet valve opened before startup. After shutdown, refilling with clean water prevents flue gas backflow and dilutes condensate.