Principle, Construction, Working, Uses, Merits and Demerits of Rotary Drum Filter

Rotatory Drum Filter

Principle

Continuous slurry and cake processing is accomplished using Rotary Vacuum Drum Filters. The RVDF is used in many different fields including waste water treatment, sludge dewatering, chemical manufacturing, pharmaceutical manufacturing, cosmetics, mineral mining and refining, and food processing. It's perfect for slurry with varying cake thickness, moisture content, and stickiness. A half-submerged drum lies in a tank of slurry. While the drum rotates, the vacuum pulls the liquid through the industrial filter, trapping the solids on the surface and creating the cake. As the drum moves through the sludge, the cake thickens.

By spraying water, air, and leftover liquor through the drum section into piping and a vacuum receiver when it emerges from the slurry tank, spray bars wash the cake. The drying zone is entered when the rotating vacuum drum filter begins to revolve toward the ceiling. The vacuum in the drum continues to suck air through the cake, further dewatering it.

Construction

It is made up of a hollow horizontal metal drum that ranges in length from 1 to 20 feet. The drum revolves at a pace of less than one revolution per minute. The drum's face is split into circumferential sectors, each of which forms a distinct vacuum cell. Internally, each sector is connected to the drum center via a revolving valve. Certain filter adjustable blocks are located on the valve. During the cycle, a valve with a bridge setting controls the vacuum, blow, and dead zone, so each sector is subjected to all of them. This aids in the discharge of the cake. The slurry is deposited in the tank. The agitator is employed to keep the slurry homogeneous. Filter cloth is fastened to the face of the drum using specific caulking strands inserted into grooved strips. Clippers are used to join the cloth ends. The filter cloth retains the cake during the cycle. The multifilament strings are strung across the breadth of the fabric. Sprays are affixed to the cake to wash it.

Working

Rotary drum filters are divided into several sections, including a pick-up area, a drain area, a cleaning area, a drying area, and a cake removal area. An agitator is used to churn the slurry, which is plunged to the desired depth to avoid particles settling to the bottom. The submerged sectors of a drum are pulled out of the water by a vacuum as the drum rotates. The drum is rotated at a certain speed to produce a cake of the desired thickness. A receiver performs the filtering. The drum enters the water wash zone after leaving the drainage zone. Cleaning is then performed with sprays. A current of air dries the cake partially, and it reaches the drying zone.

Pressure is then applied to remove the cake. A doctor's knife is used to remove the partially dried, cleaned cake. The cake can also be discharged through a belt discharge filter or a string discharge filter. The string discharge filter has countless threads strung across its width. Sticky cakes are processed with string discharge filters. They wear less quickly in this case. Belt discharge filters employ short, continuous belts. High filtering rates are possible with belt discharge. A single drum cycle accomplishes all of these tasks. Slurry is then pumped back into the drum. The pre-coat filter may be used when the solids in the slurry are too high to prevent the filter cloth from becoming clogged.

Uses

• In the production of antibiotics, a rotating filter is employed to separate the mycelium from the fermentation liquid.
• Calcium carbonate, magnesium carbonate, and starch are collected using these.
• It is appropriate for slurry having significant levels of particles in the range of 15-30%.

Merits

• Continuous rotation of the filter is required.
• This filter is ideal for filtering slurries with a high solids content.
• Because of the automated operation, labour expenses are extremely cheap.
• A rotating filter is appropriate for filtering of highly concentrated liquids or thick slurries comprising 15-30% solids.
• The cake thickness may be varied by varying the rotational speed.
• Extremely large capacity.

Demerits

• A complex design with a lot of moving elements.
• It is rather expensive since several accessories are associated with it, like vacuum pumps, vacuum receivers, slurry pumps, and agitators.
• Because the cake cracks when vacuumed, cleaning and drying are ineffective. 4. Because a vacuum is used, it is not suited for liquids nearing boiling point.
• Gelatinous or slimy precipitates that create an impermeable cake will not separate from the fabric cleanly.

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