Ways Of Filtering Dust

By Author: Scott Lintern
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Dusts are common elements of industrial air. They are available in the air but they mix with air and make them invisible. Then the air becomes foggy. This foggy air is health hazardous. So it is important to make the air filtered to make it dust free.

Dust filtration means make the air dust free by taking away the dusts and other gaseous elements from the air and discharged pure air into the environment. Now in the Industries maintaining air quality is considered as a must. To meet this requirement air filtration is a must. To do the filtration industrialists are now taking the help of different types of equipments, such as--

Cyclones
Scrubbers
Electrostatic precipitators
Baghouse filters

Cyclones

In these systems to remove particles dirty airstreams are flown in a spiral path inside a cylindrical chamber. Dirty air enters the chamber from a tangential direction at the outer wall of the device and forms a vortex as it swirls within the chamber. The larger particulates move outward because of their greater inertia and are forced against the chamber wall. They then slide down ...
... the wall into a conical dust hopper at the bottom of the cyclone. Through an inner cylinder the cleaned air swirls upward in a narrower spiral and emerges from an outlet at the top. From the hopper for disposal accumulated particulate dust is periodically removed.

For removing relatively coarse particulates cyclones are best. They can achieve efficiency of 90% for particles larger than about 20 µm (0.0008 inch). Cyclones are not sufficient to meet stringent air quality standards. They are typically used as pre-cleaners and are followed by more efficient air-cleaning equipment such as electrostatic precipitators and baghouses.

Scrubbers

Wet scrubbers trap suspended particles by direct contact with a spray of water or other liquid. A scrubber washes the particulates out of the dirty airstream as they collide with and are entrained by the countless tiny droplets in the spray. Wet scrubbers are available in different configurations.

An upward-flowing airstream is washed by water sprayed downward from a series of nozzles in a spray-tower scrubber. After sufficiently cleaned to prevent clogging of the nozzles, the water is re-circulated. 90 percent of particulates larger than about 8 µm (0.0003 inch) can be removed by spray-tower scrubbers.

The air and droplet mixture collides with a solid surface in orifice scrubbers and wet-impingement scrubbers. Collision with a surface atomizes the droplets, reducing droplet size and thereby increasing total surface contact area. The advantage of these devices is the lower water-recirculation rates. These devices offer removal efficiencies of about 90 percent for particles larger than 2 µm (0.00008 inch).

Among the scrubbers venturi scrubbers are the most efficient of the wet collectors and they can achieve more than 98 percent for particles larger than 0.5 µm (0.00002 inch) in diameter. On the relative velocity between the droplets and the particulates, scrubber efficiency depends. By injecting water into the throat of a venturi channel through which particulate-laden air is passing at high speed, venturi scrubbers achieve high relative velocities.

Electrostatic precipitators

Particles suspended in the airstream are given an electric charge as they enter the unit and are then removed by the influence of an electric field in an electrostatic precipitator. The precipitation unit comprises baffles for distributing airflow, discharge and collection electrodes, a dust clean-out system, and collection hoppers. To the discharge electrodes to charge the particles a high DC voltage is applied. Then they are attracted to oppositely charged collection electrodes, on which they become trapped.

Baghouse filters

A baghouse is an assembly of fabric filter bags. A typical baghouse comprises an array of long, narrow bags that are suspended upside down in a large enclosure. By fans, dust-laden air is blown upward through the bottom of the enclosure. Inside the filter bags, Particulates are trapped while the clean air passes through the fabric and exits at the top of the baghouse.

About Author:

Scott Lintern from Western Air Ducts writes about Dust Filteration. For more information on Dust Filteration please visit www.wad.co.uk