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Baghouse

The baghouse (also known as a baghouse filter, bag filter, fabric filter, or fabric collector) uses filtration to separate dust particulates from particle-laden gases. They are one of the most efficient and cost-effective types of dust collectors available and can achieve a collection efficiency of more than 99% for fine particulates. A baghouse can be engineered for almost any dust producing application under almost any set of circumstances. In the cleaning process, particle-laden gases enter the baghouse and pass through a series of fabric bags that act as filters. The bags can be made of woven or felted cotton, synthetic, or glass-fiber material in either a tube or envelope shape.

The high efficiency of these collectors is due to the dust cake formed on the surfaces of the bags. The fabric primarily provides a surface on which dust particulates collect through the following mechanisms which are (i) inertial collection in which dust particles strike the fibers placed perpendicular to the gas-flow direction instead of changing direction with the gas stream, (ii) interception in which particles that do not cross the fluid streamlines come in contact with fibers because of the fiber size, and (iii) electrostatic forces in which the presence of an electrostatic charge on the particles and the filter can increase dust capture. A combination of these mechanisms results in formation of the dust cake on the filter, which eventually increases the resistance to gas flow. The filter must be cleaned periodically.

Baghouses come in design classifications based on the manner by which the bags are cleaned: (i) the pulse jet system, which uses high-pressure air directed down into the clean side of a filter bag in order to remove the dust cake from the surface of the media, (ii) the shaker style system, which involves shaking the bags in order to mechanically release the dust cake, and (iii) the reverse air system in which the bags are collapsed in order to mechanically shear the dust cake from the bag surface.

In mechanical-shaker baghouses, tubular filter bags are fastened onto a cell plate at the bottom of the baghouse and suspended from horizontal beams at the top. The contaminate gas streams enters the bottom of the baghouse and passes through the filter, and the dust collects on the inside surface of the bags. Cleaning a mechanical-shaker baghouse is accomplished by shaking the top horizontal bar from which the bags are suspended. Vibration produced by a motor-driven shaft and cam creates waves in the bags to shake off the dust cake.

In reverse-air baghouses, the bags are fastened onto a cell plate at the bottom of the baghouse and suspended from an adjustable hanger frame at the top. Dirty gas flow normally enters the baghouse and passes through the bag from the inside, and the dust collects on the inside of the bags. In reverse-jet baghouses, individual bags are supported by a metal cage, which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag. Bags are cleaned by a short burst of compressed air injected through a common manifold over a row of bags. The compressed air is accelerated by a venturi nozzle mounted at the reverse-jet baghouse top of the bag. Since the duration of the compressed-air burst is short (0.1 seconds), it acts as a rapidly moving air bubble, traveling through the entire length of the bag and causing the bag surfaces to flex. This flexing of the bags breaks the dust cake, and the dislodged dust falls into a storage hopper below.

Cartridge collectors are another commonly used type of dust collector. Unlike baghouse collectors, in which the filtering media is woven or felt bags, this type of collector employs perforated metal cartridges that contain a pleated, nonwoven filtering media. Due to its pleated design, the total filtering surface area is greater than in a conventional bag of the same diameter, resulting in reduced air-to-media ratio, pressure drop, and overall collector size.