Filters blog contains following filter details used in industries to clean the fluids
- Continuous vacuum filter
- Discontinuous vacuum filter
- Centrifugal filter
- Filter media
- Filter aids
Continuous vacuum filter
In all continuous vacuum filters the feed, filtrate, and cakes move at steady constant rates.
The cake is moved out of the filtering zone, washed , sucked dry and dislodged from the septum.
The pressure is between 250 and 300 mm Hg
Rotary vacuum filter
The most common type of continuous vacuum filter.
It's a rotary drum filter.
This discharge cake all take place automatically.
Constraction
It consists of cylindrical sheet metal mounted horizontally.
The drum rotates at the speed of 0.1 to 2 r/min.
Inside a cutter drum there is a second drum with a solid surface.
It is divided into separate compartments.
It is connected with an internal pipe hole, from which air and vacuum is supplied to each compartments.
Working
The drum is immersed to the required depth in the slurry, which is agitated to prevent settling of the solids, and vacuum is applied to those sectors of the drum which is submerged.
A cake of the desired thickness is produced by adjusting the speed of rotation of the drum. Each sector is immersed in turn in the slurry and the cake is then washed and partially dried by means of a current of air.
Finally, pressure is applied under the cloth to aid the removal of the cake. Removal of the washed and partially dried cake is affected by means of a doctor knife.
Advantages
- The rotary filter is automatic and is continuous in operation, so that the labour costs are very low.
- The filter has a large capacity, so it is suitable for the filtration of highly concentrated solutions.
- Variation of the speed of rotation enables the cake thickness to be controlled.
- Pre-coat of filter aid could used to accelerate the filtration rate.
Disadvantages
- The rotary filter is a complex piece of equipment, with many moving parts and is very expensive,
- In addition to the filter itself, some accessories are connected ,e.g, a vacuum pump, vacuum receivers, slurry pumps and agitators are required.
- The cake tends to crack due to the air drawn through by the vacuum system, so that washing and drying are not efficient..
- It is suitable only for straight-forward slurries.
- Initial cost of filter and vacuum filter is high.
Uses
The rotary filter for continuous operation on large quantities of slurry.
Suitable for slurry contains considerable amounts of solids in the range 15-30%.
Examples of pharmaceutical application include the collection of calcium carbonate, magnesium carbonate, and starch, and the separation of the mycelium from the fermentation liquor in the manufacture of antibiotics
Summary of the process
The drum is dipped into the slurry and vacuum applied to the outlet, which is connected to the filtrate receiver. When the cake has formed, the cake drained or partially dried by vacuum.
The drum is sprayed with water to wash the cake. Retaining the vacuum connection drains the cake and produces partial dryness then, removed by a doctor knife.
When the solids of the slurry are too much that the filter cloth becomes blocked with the particles, a pre-coat filter may be used. A pre-coat of filter aid is deposited on the drum prior to the filtration process.
Discontinuous Vacuum Filler
Pressure filters are usually discontinuous.
This filter is 1 to 3 m in diameter and 100 to 300 mm thick.
It is of some batch operation in which cake must be dried before discharge.
It is made of corrosive resistant material.
Centrifugal Filters
A centrifuge consists of a basket in which mixture of solid and liquid , or mixture of two liquids is rotated at high speed so that it is separated into its constituents by the action of centrifugal force.
Types of baskets
A- Imperforated, in which the liquid is removed through a skimming tube, while the solid particles, sediment to the wall.
In pharmacy, the centrifuge is commonly used for drying crystals and for separating emulsions into their constituent liquids. B- Perforated basket, in which the liquid passes out through the holes.
1-The perforated basket centrifuge:
A vessel about 1m. in diameter and its outer wall is perforated. It is mounted on a vertical shaft by means it can be rotated at a high speed. An outer casing with an outlet collects the liquid thrown out from the basket.
The drive motor may be below the centrifuge and it is called under-driven,Other form is over-driven,.
Advantages of a centrifuge:
- It is very compact, occupying very little floor space
- It is capable of handling slurries with high proportions of solids
- The final product has generally, a very low moisture content if compared to a filter cake of a similar material.
Disadvantages
- It is Batch process
- It involves a considerable labor cost, making the process expensive.
Filter Media
A media filter is a type of filter that uses a bed of sand, peat, shredded tires, foam, crushed glass, geo-textile fabric, crushed granite or other material to filter water for drinking, swimming pools, aquaculture, irrigation, storm water management and other applications.
Filter media is anything placed in a filter that changes the quality of water flowing through it.
Filter Aids
"Filter Aids" is a group of inert materials that can be used in filtration pretreatment. There are two objectives related to the addition of filter aids.
One is to form a layer of second medium which protects the basic medium of the system. This is commonly referred to as "precoat".
- Coal Filters
- Sand Filters
- Cloth Filters
- Ultra Filters
- Membrane Filters
- Filter Press