Scroll centrifuge

For scroll centrifuges having back-drives, Pgp is the back-drive power ... 

Disk machines having nozzles to discharge the solids phase through small backward-pointing nozzles must have this power included in the calculations. Some thickening scroll centrifuges also use such nozzles, usually with an intermittent flow. Pp] is the nozzle power ... 

The stress resulting from the axial forces must be considered in analyzing the parts which resist axial separation, such as bolts, nuts, rings, etc. On scroll centrifuges the axial force owing to the axial component of the conveyor torque must also be considered. 

Scroll centrifuges discharge solids continuously and usually drier than disk and imperforate batch types. Generally disk centrifuges have the highest values of Z or KQ for a given size and therefore the best ability to collect fine particles at a high rate. 

Figure 3.5 Clarifying decanter (horizontal scroll centrifuge). Source Courtesy of Westfalia Separator Ltd.

Decanter Centrifuges The decanter centrifuge (also known as the solid-bowl or scroll centrifuge) consists of a solid exterior bowl with... 

Practical operation of a sludge separator, of course, requires that the solids be heavier than the liquid and not be resuspended by the action of the conveyor. A modification known as an axial-flow conveyor centrifuge (described later) is more effective in separating fine light solids than the full-scroll centrifuge shown in Fig. 30.44. Even so, the liquid effluent from these machines is usually not completely free from solids and may require subsequent clarification. Within these restrictions sludge separators solve a wide variety of problems. They separate fine particles from liquids, dewater and wash free-draining crystals, and are often used as classifiers. 

In a full-scroll centrifuge (Fig. 30.44) the liquid flows in a spiral path against the motion of the conveyor. Under these conditions the boundary layer is as much as 10 times as thick as it is when the layer flows only in an axial direction. Furthermore, spiral flow induces eddies and turbulence in the boundary layer, impeding sedimentation with axial flow the boundary layer is in laminar flow, and sedimentation is unimpeded. Willis and Shapiro give E values for axial-flow centrifuges. The addition of vanes can increase E by 3 to 4 times. 

A froth treatment process is used to remove water and fine solids from the froth (8, 9, 30, 32, 35). The froth is first diluted with heated naphtha in about 1 1 volume ratio. The diluted froth is then centrifuged in scroll centrifuges (at about 350 x g) to remove coarse solids (greater... 

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