BOKELA Ingenieurgesellschaft für Mechanische Verfahrenstechnik GmbH

Backflush Filters



The BOKELA Backflush Filter / Polishing Filter is an automatically operated pressure filter. It is used for the clarification / polishing filtration of high liquid flow rates with a low level of solid impurities (typical range: 100 – 300 mg/l). The filtration is performed at up to 5 bar in a pressure vessel equipped with special components. The filtered impurities are discharged from the filter cloth by a filtrate backflush and removed from the vessel as thickened sludge. The filtrate is nearly particle-free.

The BOKELA Backflush Filter has an advanced mechanical design and process design. It stands out with a high throughput capacity, an optimal operation and a high economy. The main characteristics are:

  • high specific throughput
  • low concentration of solids in the filtrate
  • complete cake discharge thanks to optimised backflushing
  • concentrated sludge at the discharge
  • fully automated and simple operation
  • completely closed and clean operation

The BOKELA Backflush Filter is available with up to 500 m² filtration area.

Process Design

The main components of the BOKELA Backflush Filter are the pressure vessel, the filter elements, a filtrate receiver for backflushing, quick opening/closing pneumatic valves and a process automation. The quasi-continuous operation of the Backflush Filter consists of following cycle steps:

  • vessel filling and pre-filtration
  • clear filtration
  • filtrate backflushing for cake discharge and sludge output

Performance Data

  • high specific throughput of up to 1.4 – 2.0 m³/m²h (depending on the application)
  • low solids content in the filtrate: ≤ 10 mg/l (depending on the application)
  • complete cake discharge thanks to optimised backflushing
  • concentrated solids at the discharge with approx. 150 g/l (depending on the application)
  • short pre-filtration and backflushing, i.e. short dead times
  • high availability

Filter Data

  • filtration area of up to 500 m²
  • compact unit with up to 8 m² filtration area per 1m³ vessel
  • filtration pressure of up to 5 bar, abs
  • fully automated and simple operation
  • hermetically closed and clean operation
  • stable, optimised filtration elements with optimised mechanic and process design
  • quicker and safer solids output thanks to:
    • quick moving pneumatic valves with high reliability
    • angle of output cone adapted to the product (65-75°)
  • long cloth lifetime (depending on the application)
  • small footprint thanks to high specific filtration area

The BOKELA Backflush Filter is applied for clarification of high flow rates of low-concentrated process liquids. Main field of application is the clarification of aluminium hydroxide solutions in the Bayer process.

Typical applications are:

  • aluminium hydroxide as basic material (smelter grade alumina)
  • aluminium hydroxide for chemical applications (chemical grade alumina)
  • liquids from the production of filter aids
  • process liquids from the chemical, food, pharmaceutical and life science industry

 Lab and pilot tests guarantee a reliable scale-up and sizing of the production plant.

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