The Rotary Drum Filter is a type of filter that separates solids from liquids and gases. It is a type of continuous process filter, which means that it can be used for continuous filtration. It is used in chemical or pharmaceutical industries.Â
Construction
Shown in the diagram is a rotary vacuum drum filter. It consists essentially of a cylindrical sheet metal drum mounted horizontally. It may be from 50 to 450 cm in diameter and 50 - 800 cm long. The outer surface of the drum is formed of a perforated plate. A filter medium such as canvas covers the outer side or surface of the drum that turns at 0.1 to 2 r/minute in an agitated slurry through. Inside the outer drum, there is a smaller drum with a solid surface.
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The annular space between the two drums is divided into several compartments or sectors by radial partitions and a separate connection is made between the sector and a special type of rotary valve. As the drum rotates, vacuum and air are alternately applied to each compartment.
Apart from cast iron, other materials of construction include stainless steel, titanium, plastics such as PVC, etc. These materials give much-improved corrosion resistance for many slurries.
Working Principle
The drum is immersed to the desired depth in the slurry which is gently agitated to prevent the settings of the solids. A vacuum is applied to the portion of a drum that is submerged in the slurry through the rotary valve. Because of this, the liquid is sucked into the compartment, and solids get deposited on the cloth to form a cake of desired thickness which can be regulated by adjusting the speed of the drum. With higher speeds, the thinner cake will be formed and consequently, a high rate of filtration will be achieved. The filtrate from the compartment then goes to a filtrate collecting tank through an Internal pipe and a rotary valve.
As the portion of the drum on which the cake is made comes out of the slurry, the cake is washed by spraying wash liquid. The wash liquid leaves the filter through the rotary valve and is collected separately in a separate tank. After washing, the cake enters into a drying zone as the drum rotates where the cake is partially dried by sucking air through the cake of solids.
After the cake of solids has been sucked as dry as possible, the vacuum is cut off and the cake is removed by scraping it off with an adjustable doctor s knife. A little air is blown in under the cloth to aid the removal of the cake. Once the cake is dislodged from the sector of a drum it re-enters the slurry and the cycle is reported.
Commonly, 1/3 of the cycle is used for filtration, 1/2 for washing and air drying, and 1/6 for the removal of cake.
Types of Rotary Drum FiltersÂ
The rotary drum filter is a type of filter that is typically used in the chemical industry to remove solid particles from a liquid or fluids. There are 3 types of rotary drum filters.Â
1. Rotary Vacuum-Drum filter - commonly used in the chemical industry.Â
2. Tubular drum filter - commonly used in the paper industry.Â
3. Boxed drum filter - commonly used in the food industry.
Advantages
1. This filter is entirely automatic in action and the manpower requirement is very low.
2. With a cake consisting of material solids, it is possible to remove the liquid from the cake before discharging.
3. Large capacity size, and used in filtration of large quantities of free filtering material.
4. It is possible to build up cakes of varying thicknesses. With fine solids, the thickness of the cake is small and is large with material solids.
Disadvantage
1. The maximum available pressure difference is limited as it is a vacuum filter.Â
2. As it is a vacuum filter, the difficulty is encountered in the filtration of hot liquids because they tend to boil.
3. They can not be used for materials forming relatively impermeable cakes or that cannot be easily removed from the cloth.
4. The initial cost of filter and vacuum equipment is high.Â
Also Read: Types of Filtration Equipment Used to Chemical Industry
Sedimentation Definition, Process, and Lab Batch Test
Leaf filters working Principle and Coagulation
Types of Industrial Filtration and Derivation Equations
Take these Notes is, Orginal Sources:Â Unit Operations-II, KA Gavhane