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Centrifugal or Air-Operated Diaphragm (AOD) Pumps For Ash and Slurry Handling
Power plants include many pump applications for the transport and dewatering of ash and limestone slurries. Ash in coal-fired plants is frequently transported away from the furnace by ash sluice pumps. Limestone slurry is commonly used in Flue Gas Desulfurization (FGD) scrubbing systems to remove SO2 from flue gas. Separate systems called Selective Catalytic Reduction (SCR) systems are used to remove NOx using various forms of ammonia and a catalyst. Diatomic nitrogen and water are by-products.
Pumps used in these slurry applications can include rubber-lined or hard-metal centrifugal pumps, or AOD pumps that are suitable for handling slurries with high solids content. The flow rates for these pumps can be high, in the range of 40,000 gpm or higher for slurry re-circulation in a typical FGD absorption tower found in a 400MW power plant. Lower flow rates in the range of 750 gpm apply for bleed slurry pumps. In a typical power plant, there may be (4) or more slurry recirculation pumps, and (2) bleed pumps. The number of pumps will vary with plant size and design.
An increasing number of power plants situated in coastal areas are adopting seawater flue gas desulfurization (SWFGD) in lieu of the more traditional wet-limestone process. Advantages of SWFGD include lower cost (no limestone or limestone handling equipment is required), and there is no effluent other than the seawater which requires minimal treatment other than pH balancing before re-introduction to the environment. High-capacity centrifugal pumps for handling seawater are used in the application.
Suppliers of slurry pumps include Andritz, Duchting, Flowserve, Hazelton, ITT Goulds, KSB, Lawrence, Sulzer, Weir Minerals (Warman, GEHO), Verder, Wernert, and others. |
