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BHS Filtration
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Rotary Pressure Filter

General Description

The BHS Rotary Pressure Filter is a continuously operating unit for pressure filtration, cake washing and drying of slurries up to 50% solids."   

Filtration is conducted via pressure of up to 6 bar.  Positive displacement washing, reflux or counter-current washing follows filtration.  Multiple washing steps as well as solvent exchanges, steaming and extraction can also be accomplished.  Finally, the cake is dried by blowing hot or ambient-temperature gas through the cake. 

The Filter has a uniquely designed discharge system, which provides for atmospheric discharge from pressure filtration. After automatic cake discharge, the filter cloth is washed; the clean filter cloth the re-enters the feeding / filtration zone thereby continuing the process.  All solvent and gas streams can be recovered separately and reused in the process to minimize their consumption.
The BHS-Rotary Pressure Filter works on the principle of cake filtration and is designed for the following operating parameters:

Criteria Download PDF BrochurePDF
  • Pressure design up to 6 bar
  • Cake thickness up to 185 mm
  • Operating temperatures up to 200°C
  • Filtration capacity from several kilograms/hour to
  • over 85 tons/hour of dry solids 
  • Solids content up to 50% and higher by weight
  • Particle size distribution from 1 – 2 microns to over 200 microns
rotary

Technical Description

Filtration
The filter drum rotates at infinitely variable speed in a pressure resistant housing. The annular segment between filter drum and housing is sealed at the side by stuffing boxes or air-seal chambers. Radially, sepa-rating elements divide the housing into pressure-tight chambers. The drum surface is made up of filter cells connected to the control heads by outlet pipes.

Operating Principle

 

The feed suspension enters each cell, under constant pressure, to form a filter cake. Internal divisions called separating elements of the housing allow the cake to be processed in completely separate zones. Each zone can operate under different pressures depending upon the compressibility of the cake at each stage of filtration, washing and drying.

Pressure filtration is conducted up to a maximum differential pressure of 6 bar. Pressure filtration has the added benefit of eliminating post-precipitation of the solids if the process solvent is prone to flashing under vacuum filtration.

A second benefit of the slow-rotating pressure filtration is the reproducible cake depth and the ability to control the residence time (by the speed of the drum). The slow rotation results in much lower maintenance and energy costs.

Positive displacement washing or counter-current washing follows filtration. The design of the pressure cells, such that they have no free-space and are completely filled, eliminates the possibility of cake cracking or bypass, providing maximum washing efficiency. Multiple washing steps can be accomplished along with solvent exchanges, steaming and extraction.

The cake then undergoes a drying step by blowing ambient temperature or hot gas through the cake. The control of this drying step is influenced by gas flow, pressure, temperature as well as the cake depth and residence time.

Finally, the pre-dried cake is continuously discharged. The cake is at atmospheric discharge, which allows it to be fed directly into the downstream equipment, without the need for vacuum locks or venting tanks. The cake discharge is assisted by a gas blowback, either pulse or continuous. In some cases, gas jet nozzles can be used for maximum discharge for sticky products.

Cake discharge

After cake discharge, there is a cloth rinse step. This is controllable depending upon the product discharge, filter media and potential of cloth blinding. There are several options available for this step such as spray jets and rotating nozzles and gas blowback. The cloth wash can be done after each discharge or on an intermittent basis. With the drum rotating, after the cloth rinse step, the cells are ready to be filled for filtration.

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Applications

Dyes and pigments

Most dyes and pigments are extremely difficult to filter. High throughputs, good washing results and excellent residual moisture levels are achieved in a continuous process under gentle pressure with thin cakes.

Bulk and final pharmaceutical products

In general, these products require good washing and dewatering in fully contained systems. The filters are designed to satisfy GMP requirements.

Plastics

Fine and coarse  polymers and crystals can be washed and dewatered with optimum results. High-performance filters are capable of achieving throughput rates of 85 tons/hour of dry solids. 

Agricultural, speciality and fine chemicals

The rotary pressure filter meets the stringent requirements for operator safety and containment of toxic products.

Foodstuffs

Needle-like and fragile crystals are processed without breaking and under complete containment without contact with air.

Cellulose products

Even the most difficult-to-process products are filtered, washed and dewatered in the specified temperature range, without the problem of gel formation.  These include methylcellulose, CMC, cellulose derivatives and various starches.  

Inorganic and organic chemicals

Many other products are also processed on rotary pressure filters. These include carbonates, phenols, amines, paraffin wax, zeolites, etc. 

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Technical Data

   type Filter
area
in m2
Drum
diameter
in m
Dimensions
(WxHxL)
in m
Weight
appr.
kg
   T 0.12 0.50 1.0 x 0.9 x 1.6 900
   K3 0.54 0.75 2.0 x 1.9 x 1.8 3300
   K6 1.08 0.75 2.3 x 1.9 x 1.8 3700
   A6 1.44 1.00 2.5 x 2.1 x 2.2 5900
   A9 2.16 1.00 2.7 x 2.3 x 2.2 7300
   A12 2.88 1.00 3.3 x 2.4 x 2.5 8500
   B9 3.20 1.5   3.1 x 2.9 x 3.2 11500
   B12 4.32 1.5   3.7 x 3.0 x 3.2 14000
   B16 5.76 1.5   4.0 x 3.0 x 3.2 17500
   X16 6.7 1.8   4.2 x 3.2 x 3.6 21000
   C16 7.68 2.0   4.3 x 3.4 x 4.0 23500

Typical Materials

  • Metallic materials in contact with the product: 304  stainless steel and higher grades
  • Packing and Seals:  Resistant materials such as EPDM, PTFE, Viton, aramide, etc.
  • Filter Cloth: textile filter cloths, single layer metal or multilayer media

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