16 - Dust Collectors

Abstract

The basic operations performed by dust-collection devices are separating particles from the gas stream by deposition on a collection surface; retaining the deposited particles on the surface until removal; and removing the deposit from the surface for recovery or disposal. The separation step requires the application of a force that produces a differential motion of the particles relative to the gas, and sufficient gas-retention time for the particles to migrate to the collecting surface. Most dust-collection systems are composed of a pneumatic conveying system and some device that separates suspended particulate matter from the conveyed air stream. The more common systems use either tilter media or cyclonic separators to separate the particulate matter from air. Fabric-filter systems, commonly called bag-filter or bag house systems, are dust-collection systems in which dust-laden air is passed through a bag-type tilter. The bag collects the dust in layers on its surface and the dust layer itself effectively becomes the filter medium. The principal mechanisms of disposition in dust collectors are gravitational deposition, flow-line interception, inertial deposition, diffusion, deposition, and electrostatic deposition. During the initial operating period, particle deposition takes place mainly by inertial and flow-line interception, diffusion, and gravity.