Bag Filter*

Equipment for gas or liquid clearing.

In liquid applications, bag filters are used for straining/classification of slurries to remove particlulates down to a specific size. A high porous (> 80%) polymer felt or woven textile in the form of a bag is used to trap particles above a certain size whilst allowing finer particles to pass through largely unhindered.

The simplest arrangement comprises a single bag that is attached over the end of a pipe. Dilute feed suspension is pumped through the pipe and into the bag until the pressures generated become excessively high and/or separation rates become excessively high and/or separation rates become unacceptably low, when the flow is interrupted and the bag changed manually ( and then often discarded).

In more sophisticated versions, mutiple bags are attached to a manifold system and the whole assembly is placed inside an enclosed vessel.

Although suited to a wide range of slurries, unless special precautions are taken bag filters are not generally used with toxic or volatile feeds as some spillage occurs when the bag(s) are replaced. The fabric use to form the bag must be carefully chosen, in terms of pore size, to avoid undesirable blinding by particles.

Bag filters are also used in larger scale separations involving more concentrated particle/gas mixtures.

*This definition of "Bag Filter" was reprinted by permission from the "Dictionary of Filtration and Separation". The "Dictionary" contains over 1500 definitions and 400 diagrams and photos. More information on the "Dictionary" and order form can be found here.

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