Rotary Vacuum Drum Filters

Rotary Vacuum Drum Filters

Rotary Vacuum Drum Filters

The Vacuum Drum Filters has a broad field of application, amongst others in ore refining, hydrometallurgy, metallurgic, chemical and pharmaceutical industry, food processing and waste water treatment.

A rotary drum vacuum filters (RDVF) is a continuous filter wherein the solid constituent in a pulp or slurry is separated by a porous filter cloth or other media rotated through the pulp or slurry, with vacuum applied to the inner surface to cause the solids to accumulate on the surface as a cake or layer through which the liquid is drawn.

How it works :

The process cycle of the RDVF is continuous. Each revolution consists of cake formation, cake washing (if required), drying and cake discharge.

As the drum rotates - partially submerged in the slurry - vacuum draws the liquid through the filter medium (cloth) on the drum surface which retains the solids. The vacuum pulls air (or gas) through the cake and continues to remove liquid as the drum rotates. If required, the cake can be washed prior to final drying...and discharge.

Product Range and Application :

The rotary vacuum filters can discharge its filtered cake by means of any one of several discharge arrangements. Normally a discharge device will be selected based on the process material characteristics and how readily it is released from the filtering media.

The Precoat discharge is used when direct filtration against a cloth medium is not possible because the cake cannot be removed from the cloth or when blinding is indicated. It is typically used :

The Scraper discharge is used:

For fast filtering materials.

The Roll discharge filter is usually fitted with a very tight filter medium to retain very small particles and is used :

For discharging very thin, sticky (tacky) cakes.

Discharge Methods :

Belt Discharge Precoat Discharge Roller Discharge
     
 
Scraper Discharge    

 

Rotary vacuum filters type FTV with cake discharge by blowback, belt, string, roll, precoat. Manufactured in plastic, PRFG, completely metallic with filtering surfaces from 0.5 to 60 sqm. Special application for yeast filtration.

The rotary drum vacuum filters are composed by a horizontal cylindrical drum divided into sections connected by means of pipes, to a distribution valve. The drum, covered by a filtering cloth in in polypropilene or other synthetic material lying on drainage grids manufactured by in polypropilene or different materials, rotates, at variable speed, partially immerged in a tank equipped with agitator in order to maintain in supension the slurry to be filtered. During rotation the drum is divided in four separate areas by means of the bridges foreseen inside the valve, that are : filtration area corresponding to the submerged part of the drum, washing area, drying area and cake discharge area.

Cake discharge is carried out in different manners according to the cake characteristic; the filtrate and drawn air are separated in filtrate receiver; the liquid is sucked by an extraction pump or discharged by a barometric column system while air is drawn out by the vaccum pump.

The cake is lifted off the cloth by compressed air blowing at low pressure into the discharge section. The cake is collected by knife, slides on it and falls into a belt or screw conveyor.

This type of filter is used in the treatments of slurries with a high percentage of solid content and a good permeability with cakes 3-4 mm. thick at least.

Operation:

Precoating the entire surface of the drum up to a thickness of 100 mm of Diatomaceous Earth, or other filter aid.
Filtration of the liquid across the precoat, on the surface of which the solide to be separated are deposited.
Removal of cake, at each turn of the drum, by a knife which moves forward automatically and micrometrically.
The precoat filter is mainly used for :
filtration of liquids with the aim of obtaining clear filtrates.
filtration of liquids containing highly obstructive solids.

In the discharge area the cake is compressed by a roll parallel to the drum having same length as the drum, smaller diameter and rotating at the same peripherical speed.

The cake leaves the surface of the drum and adheres to that of the roll. It finally detaches from this latter with the help of a knife and falls into a belt or screw conveyor.

This type of filter is used  when cakes no thicker than 2 mm are formed and which, from laboratory tests appear to adhere, better to the roller (usually rubbelined) than to the filter cloath.

The filtering cloth, as a continuous belt, is stretched between the drum and a series of rollers. A regulation system continuously centers the cloth over the drum and on the roller while rotating.

After filtration, the cloth detaches itself from the drum and thus the cakes falls by gravity into a belt or screw conveyor.

After spray washing with a solution at high pressure, the cloth wraps itself once again around the drum, and is ready for filtration.

This type of filter is used in the treatment of slurries which clog the cloth due to crystallization or deposits and which therefore require a continuous washing of the same.

A series of strings are stretched over the filtering cloth on the surface of the drum and between the drum and the two rollers.

After filtration the strings detach the cake from the surface of the drum thus making it fall by gravity into a belt or screw conveyor.

This filter is used for filtering slurries which give rise to fibrous cake that will not be cut  by the strings.

Rotary Vacuum Drum Filters

Hyflow single cell rotary drum vacuum filter type FTV / B

The hyflow FTV/B is a compact rotary drum vacuum filter with blow back discharge completely manufactured in high quality steel in accordance with customer and process requirements. This rugged filter of very simple design and very accurate construction minimize the maintenance problems and offers operating & performance results not found within the scope of conventional filters.

Some of the relevant characteristic of FTV/B filter, as shown in the sketches are listed below :

single cell construction with fully perforated drum surface correspond to a porosity 4 to 10 times a conventional filter.
93% of the filtering surface is constantly under vacuum.
Unrestricted filtrate and gases removal correspond to a maximum differential pressure across the cake.
High speed of the drum up to 10 times faster than a conventional filter.
Thin filter cakes that correspond to better washing; no cracking; lower residual moisture and possibility to handle sticky cakes.
Blow back discharge with no parts in contact with the drum and small filtering cells correspond to a complete discharge of the cake and filter cloth renewal (pulsating operation for very difficult products.)
Counter current washes possibly be means of internal wash collection pans.
No agitator required due to the special shape of filter tank and upward flow of liquid to be filtered.
Size of filter 1/5 to 1/7 smaller than the conventional filter allow a completely closed and pressurized construction with up to 100% closed loop that allow the use with hazardous or toxic materials requiring inert gas envelopes.

 

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