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Hi-Bar Oyster Filters

Oyster Filters are available in sizes of up to 13 m² filtration area on drum filters and up to 24 m² filtration on disc filters.

Process Design

The BOKELA HiBar Oyster technology consists of a modern high capacity filter installed in a hinged pressure vessel that opens and closes like an Oyster. This concept enables a very compact design with an incomparable accessibility of all the components for maintenance, cleaning and filter cloth change.

Like for the Standard Design, the slurry is pumped into the filter trough where the filtrate goes out through the control valve and the filter cake is discharged by a special sluice. Up to 7 bar, abs are applicable for the Pressure Filtration as well as for the Steam Pressure Filtration. The Steam Pressure Filtration additionally enable to reach very low residual moistures in the filter cake.

HiBar Steam Pressure Filtration

The patented HiBar Steam Pressure Filtration is a hybride process combining a mechanical and a thermical drying process, thus using synergy effects leading to extremely low cake moistures and very effective cake washing. The filter cake enters a specially designed steam cabin immediately after emerging from the slurry. Here, a superheated steam atmosphere exists and the following phenomenon take place which can be described by the model of the condensate front:

  • The steam condenses on the “cold” cake surface and a condensate front is built moving through the cake as a homogeneous condensate layer in a piston like flow.
  • The moving condensate front replaces nearly 100% of the mother liquor.
  • When the condensate front reaches the filter cloth, the filter cake has nearly reached the steam temperature. At this point the cake leaves the steam cabin.
  • Now compressed air passes the pre-dewatered and hot filter cake causing a very effective thermal drying which leads to extreme low cake moisture contents.

The advantages are:

  • extremely low residual moistures
  • highly efficient cake washing
  • extraction of soluble elements from the filter cake
  • reduction or even avoiding of the cracks in the cake

The steam cabin partly covers the filter and builds a separate room within the pressure vessel. Whereas the pressure vessel is filled with pressurized air or inert gas, the area inside the steam cabin consists of pure steam atmosphere.

Apparatus Characteristics

  • compact design with small footprint
  • closed apparatus
  • automated opening/closing of the pressure vessel
  • pressure range: up to 7 bar, abs (up to 17 bar, abs for specific applications)
  • temperature range: up to 150 °C
  • innovative BOKELA rotary filter technology: drum and disc filters with unique hydraulic capacity
  • drum filters with individual, exchangeable cells available
  • complete cake discharge by air blow back without cake re-wetting
  • high process flexibility for adaptation to changing product characteristics thanks to:
    • individual pressure regulation of all process zones
    • variable cake thickness range: 5-120 mm
    • variable steaming zone
  • all drives inside the pressure vessel
  • lubrication with water only (neither oil nor grease required)
  • quick filter cloth replacement, especially with the single cell design
  • high availability
  • well-proven sluice technology for both abrasive and non-abrasive products
  • cleaning in place system
  • fully automated operation from filter start to filter stop
  • stress less implementation in the plant automation
  • wide range of construction materials (stainless steel and special alloyed steels

Filter Sizes

Type of Oyster Drum FilterXS1XS2  S4  S5  M7  M9 M11  M12
Drum diameter
Filtration area
Type of Oyster Disc FilterXS1XS2XS4XS5
Disc diameter
Filtration area



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© 2011 BOKELA GmbH Karlsruhe, Germany