Cake filtration

from Wikipedia, the free encyclopedia

The cake filtration or cake-forming filtration, is a mechanical method for the separation of solids and liquids. Like cross-flow filtration, it belongs to surface filtration .

functionality

When cake filtration is a filter of a suspension is flowing. A layer of the solids to be separated accumulates on the filter over time. This layer is called the filter cake and makes a significant contribution to cleaning the liquid. As the layer to be flowed through increases, the flow resistance and thus the pressure loss increase . The driving force for liquid transport can be inertia forces (e.g. centrifugal pressure when using filtering centrifuges ) or external pressure forces (e.g. application of a negative pressure in vacuum filtration ).

The cake filtration can be carried out either continuously or batchwise .

Continuous filtration can be implemented, for example, with a vacuum drum filter. A rotating perforated drum, inside of which a negative pressure is applied, is half immersed in the suspension to be separated. The filtration process and separation take place during a drum rotation. The suspension is added continuously.

With discontinuous cake filtration, the filtering process is interrupted after a termination criterion has been reached (e.g. a certain pressure loss), the filter apparatus is opened if necessary and the filter cake is removed (often after washing and dewatering). After cleaning the filter and closing the device, filtering can start again. Discontinuous cake filtration is an unsteady and periodic process.

Continuous filtration processes are suitable for bulk goods with constant product requirements, while discontinuous processes can react more flexibly to changing requirements.

application

Cake filtration is used, for example, in wastewater treatment plants , but also in decentralized oil mills . In wastewater treatment plants, sludge can be pressed into the filter chambers of a chamber filter press by means of suitable pumps in order to separate the sludge water from the filter cake. This enables degrees of separation that are almost 100% to be achieved.

Since the flow resistance of a filter cake depends on numerous factors, such as particle size distribution , particle shape and interaction between the particles, it cannot be calculated in advance. Instead, preliminary tests are necessary to determine it.

See also

literature

  • VDI 2762 sheet 1: 2006-09 Mechanical solid-liquid separation by cake filtration; Overview (Mechanical solid-liquid-separation by cake filtration; Overview). Beuth Verlag, Berlin. ( Summary and table of contents online )

Individual evidence

  1. ↑ VDI 2762 sheet 1: 2006-09 Mechanical solid-liquid separation by cake filtration; Overview (Mechanical solid-liquid-separation by cake filtration; Overview). Beuth Verlag, Berlin, p. 4.
  2. ↑ VDI 2762 sheet 1: 2006-09 Mechanical solid-liquid separation by cake filtration; Overview (Mechanical solid-liquid-separation by cake filtration; Overview). Beuth Verlag, Berlin, p. 5.
  3. ↑ a b c Matthias Stieß: Mechanical Process Engineering 2 . Springer-Verlag Berlin, Heidelberg, New York, 1994, ISBN 3-540-55852-7 , pp. 98-100.
  4. ↑ DIN 19569-9: 2004-07 sewage treatment plants; Building principles for buildings and technical equipment; Part 9: Mechanical sewage sludge dewatering. Beuth Verlag, Berlin, p. 12.
  5. ↑ VDI 2762 sheet 2: 2010-12 filterability of suspensions; Determination of filter cake resistance (Mechanical solid-liquid separation by cake filtration; Determination of filter cake resistance). Beuth Verlag, Berlin, p. 4.