Classifiers solid-bowl centrifuge

Centrifuges. Solid-bowl centrifuges have been proposed as an alternative classifying device to hydrocydones for cut sizes below 10 JJm. The results appear to be mixed (21). In one application, where the cut size was 6.5 Jim and the sharpness index 0.7, there was essentially no apparent bypass. However, in other applications operating at higher feed concentrations, the cut size ranged from 5—8 im, but the sharpness index was between 0.3—0.5 and the apparent bypass between 10—30% or higher (22). Smaller cut sizes have also been reported (23). 

Centrifuges are operated as elassifiers, sedimentors, and filters. Centrifugal classifieation and sedimentation are carried out in solid bowl units (frequently called decanters) as illustrated in Fig. 25. Most decanters are operated on a eontinuous basis. The slurry enters as shown in Fig. 25. The solids settle out and are conveyed toward diseharge by a seroll, whieh is turning at a lower speed than the bowl. The clear liquid moves... 

Partide size and shape may be manipulated by centrifugation using a combination of solid-bowl and disk-nozzle centrifuges to classify the particles according to size. The... 

The liquid layer thickness diminishes from chamber to chamber, the further each chamber is from the bowl centre greatest in the central chamber and smallest in the outermost chamber. Hence the effective settling distance also declines from the central chamber outwards. The effective centrifugal acceleration field increases from chamber to chamber (being proportional to baffle diameter), so that with a given difference in densities and a feed liquid of a constant viscosity, the coarser solid particles will separate out in the inner chambers and the finer particles in the outer chambers. Thus the solid matter is classified to some extent, at the same time that the liquid is being clarified. 

The liquid layer at the rotating bowl wall is maintained at the desired pond depth by the location of overflow weirs. These are adjustable ports located at the closed end of the bowl. The solids are continuously moved by scroll action to and then up the conical end of the rotating bowl, out of the pond, to drain as they move up the beach. Rnally, the solids are ejected from the open end of the bowl, thrown radially into a stationary collecting chute in the machine s casing, from which they drop into a container. Decanter centrifuges can be classified into three types ... 

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