Precoat filter systems

System specification

The filter system works in accordance with the precoat principle
and can be operated with and without filter aids (without filter aids:
slotted screen filter AF special system).
The stainless steel wire or plastic elements inside the filter casing
are used as filter cake carriers.
The filter aid for precoating is homogenised in a precoating tank
with suitable precoating liquid (filtrate or slurry) and applied to the
filter elements by a pump in a closed loop. The liquid is circulated
over the elements until the filter cake has formed and the liquid
emerges completely clear from the filter. Then it is permissible to
switch to slurry infeed and filter discharge.

During the filter process, the slurry is pressed through the filter cake
and cleaned and clarified. Particles up to 1 μm fineness can be filtered
out in this process depending on the type of precoated filter
aid.
Small quantities of filter aids can be added continuously when filtering
heavily contaminated liquids in order to maintain the porosity
of the filter cake.

If the maximum permissible pressure is reached during increasing
contamination of the filter cake, the filter shall be cleaned by regeneration.
Discharge and backflushing occur simultaneously. The feed pump
is switched off if this pressure is exceeded.

Filter aid selection

The filter aid selection is essential for the clarification effect.
Consistent, uniform quality, correct particle shape and size and
minimum moisture content are important. Kieselguhr and cellulose
fibres have proved to be the best. Correctly processed, they
form skeleton-shaped, porous, odd-shapped particles which
produce the best filter effect.

Perlite, cellulose fibres and carbon products are also used as
filter aids as well as kieselguhr. We recommend the most suitable
filter aid individually for each application. 500 - 1000 g/m² filtration
surface is required, depending on the type of filter aid used.
Different filter aids can be precoated in special cases.