Share Filtration Co.,Ltd.

Media Filtration in Dust Collectors

Filter media is used to filter out dust particles from the polluted air stream, normally by using a screening material (such as fabric), placed in the path of the air stream. The dust particles stopped in the dust collector by thefilter media form a ‘dust cake’ on the incoming surface and as more dust particles collect on the filter media the thickness of the dust cake increases. This increases the efficiency of the dust collector filter media (capturing up to 99.99 % of dust particles in some cases).

The two main functions of media filters in major types of industrial dust collectors are:

1. to stop dust particles on its surface while allowing clean air molecules to pass through and
2. to provide easy release of the dust cake during cleaning.

Media filter cleaning is normally done by a burst of clean air in the reverse direction to the air stream with a velocity greater than air stream. The greater force of the cleaning air burst dislodges the dust cake from the filter media and drops it into the hopper area. For greater efficiency, a fan is used to push or pull air through filter media openings.

Methods to Improve Filtering Properties of Fabric

1. Weaving of fabric material in any of the following ways.
   1. Plain weave – Fabric can be made porous or tight by number of counts per inch.
   2. Twill weave – Has fewer weaves and is more porous and flexible
   3. Sateen weave – has least number of weaves and is porous, flexible and smooth
2. Use of needled-felt material – With its short felt fibers pressed together and mechanically fixed by needle punch machine, this material has high dust collection efficiency and flow rate.
3. Use of singed material – It improves the surface of the bag.

Dust Cake Characteristics on Bag Filters

The high efficiency of fabric collectors depends on the formation of a good filter cake. For a good filter cake to form, dust particles must have interlocking characteristics. Porous cakes increase dust collection and retains more dust and can operate at a lower pressure drop. A good mix of collectors, inlets and operational procedures can deal with any dust or powder. 
The thickness of dust cakes on baghouse collectors varies between 1/16th and 1/8th inches and on cartridge collectors the cake is less than 1/64th inch thick.

Media Filtration Aids

A ‘precoat’ of inert material applied on the filter surface helps when the dust collector contains moisture, oil and small dust particles sizes. Applying the precoat on the clean surface of the filter media forms a protective dust cake layer. The use of this type of a filtration aid helps in efficient release of the dust cake, captures small particles and increases overall efficiency. However ‘precoats’ have limited use. Frequent applications may be needed to maintain the protective coating and there could be difficulties in recycling product dust from hopper if precoat material mixes with dust. Ideally, precoats must be applied on job specific basis after considering the cost and benefits of the system.