Drainage centrifugal filtration

For cakes of high permeabihty, the capillary drain height may be an insignificant fraction of cake thickness, and film drainage becomes the controlling factor in a centrifugal field (7). Under unsteady-state conditions, equation 18 represents the drainable Liquid left in the cake as a function of the centrifugal filtration parameters ... 

Cake Dewatering. Dewatering (qv), identified as a separate entity in filtration, is used to reduce the moisture content of filter cakes either by mechanical compression or by air displacement under vacuum pressure or drainage in a gravitational or centrifugal system. Dewatering of cakes is enhanced by addition of dewatering aids to the suspensions in the form of surfactants that reduce surface tension. 

Equipment. Centrifugation equipment that separates by density difference is available in a variety of sizes and types and can be categorized by capacity range and the theoretical settling velocities of the particles normally handled. Centrifuges that separate by filtration produce drained soflds and can be categorized by final moisture, drainage time, G, and physical characteristics of the system, such as particle size and Hquid viscosity. 

Mechanical Design The vertical basket centrifuge is equipped with a cylindrical basket rotating about the vertical axis. The basket shell is normally perforated and lined with filtration media consisting of filter cloth, and backing screens to provide liquid drainage paths to the basket holes. Securing the filter cloth may be by hook and loop attachment or with snap-in retainers. 

Filtration centrifuges are used for the separation of solids from liquid slurries, chiefly in industrial applications, and are usually characterized in terms of the final moisture content, drainage time, and centrifugal force. They are most useful for high-volume... 

Sampling of interstitial waters is particularly challenging due to the potential for the sampling process to perturb the system by, for example, sorption and/or contamination from the sampler and changes in redox state and pH. Five commonly used methods are centrifugation, centrifugal drainage, basal cup, vacuum filtration, and dialysis. 

FIGURE 8.14 The scheme of filtration-flotation device. 1 unit case 2 centrifugal pump 3 drainage device 4 sand 5 pump inlet line 6 ejector 7 bubbling compartment 8 bubble-film extractor 9 water inlet 10 UV sterilizer 11 water outlet. 

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