Bag Filter.
Principle:
Particle Size and density of particles.
In a bag filter, size separation of fines (or dust) from the milled powder is achieved in two steps.
In the first step, the milled powder is passed through a bag (made from cloth) by applying suction on the opposite side of the feed entry. This facilitates the separation.
In the next step, pressure is applied in order to shake the bags so that powder adhering to the bag falls off, which is collected from the conical base.
Construction:
It consists of a number of bags made of cotton or wool fabric.
These are suspended in a metal container.
A hopper is arranged at the bottom of the filter to receive the feed.
At the top of the metal container, a provision is made for vacuum fans and exhaust through a discharge manifold.
At the top of the vessel a bell-crank lever arrangement is made to change the action from filtering to shaking.
Working:
(a)Filtering period:
During this period the vacuum fan produces a pressure lower than the atmospheric pressure within the vessel.
Gas to be filtered enters the hopper, passes through the bags, and out of the top of the apparatus.
The particles are retained within the bags.
(b)Shaking period:
During this period the bell-crank lever first closes the discharge manifold and air enters through the top so the vacuum is broken.
At the same time it gives a violent jerking action to the bags so that they are freed from the dust.
The fine particles are collected at the conical base.
Uses:
Bag filters are used along with other size separation equipment, e.g. a cyclone separator.
They are used on the top of a fluidized bed dryer for drying to separate the dusts.
They are used to clean the air of a room.
Household vacuum cleaner is a simple version of a bag filter.
Commonly Asked Questions.
With a well labelled diagram describe construction and working of “Bag Filter”.
Write a short note on “Big Filter”.