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.