Pressure Filtration with Drum Filters

BoHiBar Drum filter – for filtration, washing and dewatering of fine-grained products.

Intensive filter cake wash. Low residual moisture. Gas-tight and completely leakproof operation. Complex process conditions. Minimal footprint. Such challenges master the continuous BoHiBar drum filters with flying colors. Particularly dry solids are achieved with BoHiBar steam pressure filtration.

BoHiBar Drum filters deliver unique results in the filtration, washing and demoisturing of fine-grained or difficult-to-filter products, especially in demanding product and process conditions.

High filtration pressure differences up to 6 bar (g) ensure high specific throughputs, intensive cake washing and very low residual moisture. The closed design ensures a gas-tight, leakproof operation when high process pressures and temperatures must be maintained or contamination must be avoided. The space requirement is minimal.

For particularly low residual moisture, steam pressure filtration can be performed on BoHiBar Drum filters. This innovative hybrid process produces particularly dry solids.

BoHiBar drum filters are available in different sizes with filter areas up to 40 m2 per filter unit.

Features and benefits:

  • filtration of fine-grained, sensitive or toxic products
  • highly efficient filter cake washing
  • lowest residual moisture, especially with steam pressure filtration
  • saving of drying costs or making thermal drying redundant
  • high process pressures up to 7 bar (a) and high temperatures up to 200 °C
  • gas-tight and completely leakproof operation
  • also suitable for solvent-based suspensions
  • possibility for direct re-slurrying of the filter cake (also under counterpressure)
  • continuous, fully automatic operation

BoHiBar drum filters from BOKELA represent the most advanced technology for continuous pressure filtration.

The basic principle is also known as hyperbaric filtration and is very simple: a continuous rotary filter is installed completely in a pressure vessel filled with compressed gas of up to 7 bar (a). A pump feeds the suspension into the filter trough in the pressure vessel. The filtrate flows through the filtrate pipes to the control head of the filter apparatus and from there to the filtrate reveivers. The filter cake is discarded from the filter cloth by a reversed blast of compressed gas and discharged through solids locks from the pressure vessel.

  • filtration with high differential pressures Δp up to 6 bar (g)
  • most modern drum filters with features known and proven by the BoVac Drum filter technology (replaceable filter cells are optional)
  • operating temperature up to 200 °C
  • option of installing a steam hood for steam pressure filtration
  • closed, contamination and emission-free process chamber: gas-tight and leakproof
  • no filter cake conveyor in the pressure vessel required
  • fully automatic cleaning-in-place (CIP) system
  • vertical pressure vessel*, horizontally split and fully opening – optional automatic opening
  • fast and excellent accessibility of the filter
  • proven gate valve systems for different requirements (double gate valve, rotary valve)

*) for filter sizes up to 18 m² filter surface, drum filters with 40 m² filter surface have a horizontal pressure vessel.

On BoHiBar Drum filter, filter cakes are intensively washed with a low wash liquor requirement. Like the BoVac Drum filters, they have a hydraulically optimized filter design that meets all the requirements for intensive replacement cake wash.

The results are:

  • clean filter cake by high washout in up to 3-stage countercurrent washing
  • low washing medium consumption
  • sharp separation and separate removal of the individual filtrate streams

By applying overpressure of up to 7 bar (a) BoHiBar Drum filters offer considerably higher pressure differences for filtration and demoisturing of the filter cake than with vacuum filters.


  • low residual moisture due to intensive demoisturing
  • high solids throughputs even with fine particulate suspensions
  • smaller filter area

BoHiBar steam pressure filtration is an innovative hybrid process which releases synergies through the combination of mechanical and thermal principles of action. In order to accelerate and intensify the demoisturing process, the filter cake is treated with steam. The filter drum is equipped with a specially developed steam cabin which covers only a limited part of the filter surface up to the steam break-through point. The cake is then dried by a compressed air stream to its final moisture content. Due to the accelerated dewatering, the residual moisture of the filter cake can be halved compared to a pressure filtration.


  • extremely low residual cake moistures
  • highly effective cake washing
  • saving of drying air

BoHiBar Drum filters stand out with their most modern filter and plant design, characterized by reliable operation and ease of maintenance:

  • high availability (> 92 %) thanks to innovative design and preventive maintenance concept
  • fully automated operation with automatic startup, shutdown and cleaning procedures (cleaning in place)
  • high flexibility in operation in case of product fluctuations
  • excellent accessibility of the filter with the vessel open
  • low maintenance requirement due to innovative wear protection components
  • fast and effective maintenance of the entire system due to good accessibility and sophisticated maintenance aids
  • quick re-clothing, as no wire winding is required
Filter Type [–]
S5 M9 M13 L18 L40 XL26
Filter Area [m²] 5 9 13 18 40 26
Drum Diameter [m] 1.4 1.9 1.9 2.4 2.5 3.2
Length of drum [m] 1.2 1.5 2.2 2.4 5.3 2.6
No. of filter cells [–] 24 30 30 36 24 48

Pressure Vessel Design[–]

Pressure Vessel Diameter [m]














Crystallization and Precipitation Suspensions

Tailored Solutions for Smooth Solid Separation, Washing and Dehumidification.

In crystallization and precipitation processes, solids have to be separated from suspensions. The BOKELA filter series BoHiBar Drum and BoVac Drum allow a product-friendly, fully automatic solution for the often sensitive suspensions, while also reducing drying costs.

Plastic Precursors

Filtration Apparatuses for High Product Quality and Consistently Low Costs.

Filtration is often an important step in the production of plastics. BOKELA products such as BoHiBar Drum, BoVac Drum or BoCross Micro Screen provide reliability, long service life and excellent process results. Minimal energy consumption and reduced drying costs ensure an improved economy.

Pigments, Fillers & Dyes

BOKELA filters for Sensitive Solids and Smallest Particle Sizes.

Pigments, fillers and dyes are used very differently in the various fields of application. A feature all of them share is the very small size of particles, usually smaller than one micrometer. The technologies of the BoCross Dynamic, Boris MicroScreen, BoVac Drum and BoHiBar Drum series ensure a reliable and product-friendly separation.

Continuous Pressure Filtration

For particularly fine particles, high throughputs and very low residual moisture.

Continuous pressure filtration with a BoHiBar Disc filter is the right solution for products difficult to filter and high suspension amounts, as for example in ore, coal or mineral processing. The BoHiBar Drum filter provides excellent results with regard to filtering and washing fine-grained products and demanding process conditions.

Steam Pressure Filtration of an Organic Acid (Naphthalene-Sulphonic Acid)

This BoHiBar drum filter is operated for steam pressure filtration of an organic acid. The suspension coming from the reactor consists of organic crystals suspended in water and is enriched with salts that are completely dissolved in the filtrate.

Steam Pressure Filtration of High-Quality Pearlescent Pigments

The BoHiBar drum filter is equipped with exchangeable filter cells and is designed for steam pressure filtration It is operated to filter, wash and dewater fine-grained (x50 < 5 µm) high quality inorganic pigments.

Steam Pressure Filtration of a Crystallization Product

This BoHiBar drum filter is operated for an intensive wash and drying of an organic crystallization product by steam pressure filtration to obtain a high purity product.


Low residual moisture is important for the further processing of the filter cake. With mechanical drying, an intelligent filter design and the right operation mode, production costs can be considerably reduced.

Filter Cake Washing

Filter cake is the name for the solids filtered from a suspension and collected at the surface of the filter medium. The washing of the filter cake is essential to the purity of the filtered solids and thus, for the reusability.

Solid Separation

Solid separation is the first process step with regard to separating solids from fluids. The driving force behind the process is the pressure difference with which the suspension flows through the filter medium.

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© 2024 BOKELA GmbH Karlsruhe, Germany

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