It Makes Sense To Select A Filter Press

of When a very low moisture content is required for thermal cake drying or incineration.

rar When high fíltrate clarity is required for polishing applications.

rar When good cake release assisted by squeezing is required.

«y When the cake is disposed as land fill for spreading with a bulldozer provided it is hard enough to carry its weight.

When large filtration areas are required in a limited space.

• The shuttle shifter moves the plates one by one towards the follower and the cake discharges.

• The drip trays close and are ready for the next cycle.

• The shuttle shifter moves the plates back one by one towards the fixed header. When each plate parks the cloth is washed at 100 bar with a mechanism that lowers and lifts a pair of symmetrical manifolds with high impact nozzles.

Cake disposal is relatively straightforward. Cakes may be discharged into bins that are trucked away or transported with a belt conveyor. With very large filter presses a well formed cake may weigh 200-300 kg per chamber and when it falls into a bin or onto a belt conveyor in one solid piece the impact is very high. Hence, special measures are required to break and de-lump the sole hard cake and, for belt conveyors, it is also recommended to increase the number of belt support rollers below the discharge chute at the point of impact.

The filterpress by itself requires little maintenance however the automation features that accompany the machine should be checked regularly and with particular attention to safety devices such as:

• The infra-red curtain that protects the operator during the closure of the plate pack should stop the hydraulic pump within 2 milliseconds.

• The switch that warns when a loss of pressure in the hydraulic plate closing system detects leakage between the plates.

• The filtrate flow meter microswitch that stops the slurry feed pump when the chambers are full.

• The microswitch that is attached to the drip trays is interlocked so that the doors are fully open during cake discharge.

• The pressure switch that permits squeezing of the membranes only when the plate pack is compressed with the hydraulic closing system.

• The zippered bellows that protect the hydraulic piston against drippings should be checked for wear and tear.

• The two manifolds that wash the cloth on both sides of the plate have high impact nozzles at a pressure of 100 bar. When some nozzles of one manifold are plugged the jet impact is uneven and the plates tend to swing.

• The cloth must be checked for holes and the optional cocks on the filtrate port of each plate help in identifying damaged cloths.

• The impregnated edges that surround the cloth and seal between adjacent plates should be checked for leakage.

Body-aid (i.e., the filter-aid) and precoating are often mentioned in connection with pressure filtration and the difference in their application is: (1) Body aid is used when the slurry is low in solids content with fine and slimy particles that are difficult to filter. To enhance filtration coarse solids with large surface area are added to the slurry and serve as a body-aid that captures and traps in its interstices

The following materials can serve as body-aid or are used to form a precoat:

Diatomaceous Earth (also called Diatomite) consisting of silicaceous skeletal remains of tiny aquatic unicellular plants.

Perlite consisting of glassy crushed and heat-expanded rock from volcanic origin.

Cellulose consisting of fibrous light weight and ashless paper like medium.

■Special groundwood is becoming popular in recent years since it is combustible and reduces the high cost of disposal. There are nowadays manufacturers that grind, wash and classify special timber to permeabilities which can suit a wide range of applications.

. ____ * * i ••"■ - _- ■- .-.-- -.1 ___|_|___________

the slow filtering particles and produce a porous cake matrix. The amount added depends on the nature of the solids and varies from ? for non-compressible and up to 5 times for gelatinous solids; (2) Precoating the plates with a 2-3 mm thick medium of a known permeability and its application requires skills since it takes-up effective cake volume, lengthens the cycle time and an over consumption can be quite costly. Precoating prior to filtration serves two main purposes:

• When the contaminants are gelatinous and sticky it forms a barrier that avoids cloth blinding. Likewise the interface between the precoat and the cloth parts readily so the cake discharges leaving a clean cloth.

• When a clear filtrate is required immediately after the filtration cycle commences otherwise recirculation must be employed until a clear filtrate is obtained.

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  • hamza
    How to select a filter press?
    8 years ago

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