Cake Filtration Essay

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Cake Filtration PIERO M. ARMENANTE NJIT Cake Filtration • Cake filtration consists of passing a solid suspension (slurry) through a porous medium or septum (e.g., a woven wire). The solids in the slurry are retained on the surface of the medium where they build up, forming an increasing thicker cake. • As more slurry is filtered the solids retained on the medium provide most of filtering action. In cake filtration the cake is the real filtering element. PIERO M. ARMENANTE NJIT Cake Filtration (continued) • As time goes by the thickness of the cake increases, as more solids are filtered. This results in a corresponding increase of the pressure resistance across the cake. • If the cake is incompressible (i.e., it does not change its volume as pressure builds up) the pressure resistance increases proportionally to the cake thickness. • However, since most cakes are compressible the pressure across the cake typically increases even faster than the cake build-up. PIERO M. ARMENANTE NJIT Cake Filtration (continued) • The cake is removed intermittently during batch filtration processes. This is done by taking the filter off line and manually or automatically collecting the cake. • The cake is removed continuously in continuous processes, for example by scraping the cake with blades, as in rotating filters. • Cake washing and drying operations can also be incorporated in the operation of most filters. PIERO M. ARMENANTE NJIT Examples of Cake-Forming Filters • Filter presses • Belt filters • Vacuum filters: Rotary vacuum belt filters Rotary vacuum precoat filters Vacuum disk filters PIERO M. ARMENANTE NJIT Example of a Filter Press After Metcalf and Eddy, Wastewater Engineering, 1991, p. 869 PIERO M. ARMENANTE NJIT Cross Section of a Filter Press After Freeman, Standard Handbook of Hazardous Waste Treatment and Disposal, 1989, p.
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