The separation is performed in two stages. In the first stage, the gas-containing dust is passed through a bag (made of cloth) by applying suction and because of this separation occurs. In the next step, the bags are shaken by applying pressure so that the powder adhering to the bag falls and is collected from the base.
Construction of Bag Filter:
- A series of bags (made of cotton or wool fabric) are suspended in a metal container. In the bottom portion, a hopper is arranged to receive the feed. A bell-crank lever arrangement is provided at the top of the vessel to change the filtering action to shaking.
Working of Bag Filter:
- Filtering period: During this period the gas containing dust enters through the hopper. Then it is passed inside the bags and at the top of the apparatus. The vacuum fan produces pressure below the atmospheric pressure inside the apparatus. As a result, the particles get trapped within the bags.
- During this period, the bell-crank lever rotates and changes the position of the damper. The outside air enters through the top in the metal casing and therefore the vacuum is broken. At the same time, it causes violent shaking or jerking action to the bags. Dust or fine particles are displaced from the bags. The maximum portion of dust falls into the hopper which is withdrawn further from the conical base.
Pharmaceutical Uses of Bag Filter:
- Bag filters are also commonly referred to as fabric dust collectors that are used in large industrial units to separate dust particles from dusty gases.
- They are the most efficient and cost-effective type of industrial dust collector.
- Bag filters are considered the most efficient among all dust collectors because they can reach an efficiency level of up to 99%.
- Bag filters are also used along with a cyclone separator.
- They are used to clean the air of a room.
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