Removing Solids From Liquid-Solid Mixtures (Slurries)
|The Vacuum Drum Filter gives simplicity in operation, and is applicable to de-watering
a variety of solids, with concentrations of solids varying from 01.% to 30%. The drum revolves in a pulp-filled tank.
As drum revolves, various surfaces of the drum enter the pulp and are subjected first to vacuum cycle then the discharge
cycle. The segments of the filter drum are constructed so that the filtrate quickly and completely drains to the
over-size filtrate pipe connections and through to the vacuum system. This results in a drier filter cake
with resultant benefits.
An oscillating agitator to keep the pulp in suspension is usually installed in the filter tank. A vacuum filter valve
has a vacuum hose connection. If the vacuum filter is of the pre-coat design, for dewatering low solids slurries
(0.1% to 2% solids), it will utilize diatomaceous earth as a filter aid and the drum will be coated with the DE.
A very fine cut of the DE (0.01 to 0.001 inch) will be continuously made, removing the filter aid with the solids
recovered from the slurry. If the filter is a scraper drum or belt discharge design, it will handle 3% to 30%
solids feeds, and will have, in addition to the vacuum connection, a pressure air hose for the blow or discharge cycle.
The vacuum is for cake pick up from filter tank and for washing service where wash water filtrate is to be removed
separately. The pressure air hose provides connections through the valve to give one light blow to loosen filter
cake ahead of the scraper.
1. Oscillating Agitators. Oscillating agitators keep solid particles in the pulp in suspension and to keep entire pulp
surface moving in gentle waves against rotating filter drum to aid filtering.
2. Adjustable Scraper. An adjustable scraper is provided when required. This permits a portion of filter coke to act
as filter media to allow rapid filtering at high tonnage rates. Design refinements in coke scraping and discharge
result in substantially longer service from filter media.
3. For precoat filter, a knife scraper with automatic knife advance, continuously moves the knife 0.01 to 0.001 inches each
revolution to remove a thin section of the diatomaceous earth and the filtered solids.
4. A Vacuum Drum Filter can be supplied with washing attachment for washing contaminents from the filtered solids,
prior to their discharge, during the drying cycle. Washing sprays and hoods ore designed to provide thorough washing of
filter cake to remove soluble fraction of the filter cake or for more complete removal of filtrate.
5. Filter Valve Assembly. The filter valve is designed for simplicity and long life. Two vacuum connections ore
provided to allow removal of main filtrate and wash water. These filtrate products can be discharged separately
when desired. Two air connections can also be provided to give variation in intensity of the blow before and after the
scraper far added flexibility.
The photo at right shows a Vacuum Drum Precoat Filter. A vacuum Drum Scraper filter looks just like a precoat filter,
without the coating of diatomaceous earth on the drum face.
Illustration Of A Working Precoat Vacuum Drum Filter
||The illustration at left shows how a vacuum drum filter with scraper discharge, works. The slurry is drawn to the surface of the drum, which is covered with a filter material, holding the solids and allowing the liquid to enter the drum. The liquid is pulled by the vacuum flow, to a filtrate tank.
The vacuum is applied to the drum as the drum rotates into the atmosphere, drawing air through the solids on the drum face and further reducing their moisture content.
Then, just prior to discharge, a blast of compressed air pushes the solids away from the drum surface, so the scraper blade can scrape them off easily, without tearing the filter material on the drum surface.
||The photo at left shows complete vacuum drum filter, including the vacuum pumps, vacuum receiver, filtrate receiver, filtrate pump, drum drive mechanism tank. These small vacuum drum filters are used for small scale production, remote filtration in environmental cleanup/remediation work and for pilot plant processing.
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