Application
Compared with other methods available for degritting feed streams, FLSmidth's Dorr-Oliver® Bowl Desiltor offers lower operating cost, with less control required for its operation. It provides a packaged piece of equipment purpose-designed to perform its designated function.
The unit comprises a flat-bottomed circular tank, or bowl, incorporating rotating rakes. The feed stream enters a concentric feedwell, where hydraulic energy is dissipated and the coarser material settles out in the bowl. A peripheral overflow launder carries the fines to a discharge point. The rakes move the heavier settled grit outward to a point where a tank with sloping bottom is connected to the bowl. This tank is narrower than the bowl diameter, and is equipped with a set of mechanically-operated reciprocating rakes. Solids are conveyed up the slope by the rakes, for discharge in a drained condition.
Operation
Sizes
Dorr-Oliver® Bowl Desiltors are available from 3 to 10 meters in diameter, with either simplex or duplex rake classifier sections 460 to 1220 mm wide and 7200 mm long. The maximum oversized particle handled is about 12 mm. Feed concentrations up to 65 % solids and from 5 to 250 t/h can be handled. Normal solids content in the overflow is from 1 % to 15 %, with underflow generally from 70 % to 85 %.
Industries
This unit is used mainly in the recovery of relatively fine sand overflowing washing units in the steel, metallurgical, concrete sand, foundry sand, glass sand and limestone processing industries. It also serves as a scalper ahead of thickness or clarifiers, for reducing sand load so that conventional machines can handle the remaining finer solids. Overflow water is normally clarified in a thickener and the resulting underflow can be dewatered on vacuum drum filters. Particularly useful applications for the Desiltor include blast furnace scrubber water and BOF furnace water. In existing plants, it provides a compact piece of equipment, without the need for the higher head and pumping capacities associated with other systems such as cyclones.