Rotary vacuum-drum filter

[1] The technique is well suited to slurries, flocculated suspensions, and liquids with a high solid content, which could clog other forms of filter.

It offers a wide range of industrial processing flow sheets and provides a flexible application of dewatering, washing and/or clarification.

Applications: The advantages and limitations of rotary vacuum drum filter compared to other separation methods are: Basically there are five types of discharge that are used for the rotary vacuum drum filter such as belt, scraper, roll, string and pre coat discharge.

Roll discharged is used if the desired separation requires high filtration rate, if high solid content slurry is used or if the slurry is easy to filter to produce cake formation or if the discharged solid is sticky or mud-like cake.

The vacuum draws liquid and air through the filter media and out the shaft hence forming a layer of cake.

Solids that are trapped on the surface of the drum are washed and dried after 2/3 of revolution, removing all the free moisture.

Basically, the drum surface is pre coated with a filter aid such as diatomaceous earth (DE) or perlite to improve filtration and increase cake permeability.

It then undergoes the same process cycle as the conventional rotary vacuum drum filter however, pre coat filtration uses a higher precision blade to scrape off the cake.

Typically, the output is in the units of pounds per hour of dry solids per square foot of filter area.

Rotary vacuum filters are flexible in handling variety of materials therefore the estimated solids yield from 5 to 200 pounds per hour per square foot.

For pre coat discharge, the solid output is approximately 2 to 40 gallons per hour per square foot.

In addition to operating at lower vat level, the flow rate per drum revolution decreases and ultimately thinner cake formation occurs.

At steady operating conditions, adjusting the drum speed gives a proportional relationship with the filter throughput as shown as in figure 2.

The belt tension, de-mooning bar height, wash water quantity and discharge roll speed are carefully tuned to maintain a good path for the cake formation to prevent excessive wear of the filter cloth.

Adjust duration of blow back pressure short enough to remove the cake from the filter cloth.

Select filter cloth to obtain solid binding resistance and good cake release.

Adjust the scraper knife to leave a significant heal on discharge roll to produce a continuous cake transfer.

Have ceramic tube place over each aligning tine bar to act as bearing surface for the strings.

The table indicates the number of hours that the filter can operate in a one-inch pre coat cake; the required condition is that the advance blade must be at a constant position.

If the operating parameter is higher than the optimum range, the user can reduce the knife advance rate and use a tighter grade of filter aid.

This process eliminates the odour of the stream but result in slightly acidic product due to the effect of carbon dioxide present.

However, a smaller design would be more economical as the maintenance, energy usage and investment cost would be less than a bigger rotary vacuum drum filter.

Over the years, the technology drive has pushed development to further heights revolving around rotary vacuum drum filter in terms of design, performance, maintenance and cost.

This has also led to the development of smaller rotary drum vacuum filters, ranging from laboratory scale to pilot scale, both of which can be used for smaller applications (such as at a lab in a university) [10] High performance capacity, optimised filtrate drainage with low flow resistance and minimal pressure loss are just a few of the benefits.