Dust Control Handbook for Industrial Minerals Mining and Processing

AIR CLEANING DEVICESAir cleaning devices used within the industrial minerals mining industry are used to cleanventilation airstreams of harmful particulate matter. The choice of air cleaner for any particularinstallation will depend on the following:dust concentrations and dust characteristics,particle size,efficiency of particulate removal required,airstream temperature, airstream moisture content, andmethods of disposal.Distinguishing dust characteristics that affect the collection process include abrasive, explosive,sticky or tacky, and light or fluffy. The shape of the dust particle is also important because itfactors into whether the particles are agglomerating (irregular) or nonagglomerating (spherical),which is important when using a filter cloth. For collection purposes, agglomerating particles areideal as they allow dust cakes to build up easily on the filter cloth, allowing for more efficientcollection at the dust collector. However, agglomerating particles may have a tendency to notrelease from the filter cloth very easily.The types of dust control equipment used for air cleaning range from very crude gravityseparators to more sophisticated electrostatic precipitators. The following is a list of the types ofcollectors used for particulate removal.1. Gravity separators (drop-out boxes).2. Centrifugal collectors or cyclones.3. Baghouse collectors.4. Cartridge collectors.5. Wet scrubbers.6. Electrostatic precipitators (ESPs).A brief overview of each type of collector, along with its advantages and disadvantages, follows.Gravity Separators (Drop-Out Boxes)Gravity separators (also called drop-out boxes) are large chambers where the velocity of theairstream is drastically reduced in order to facilitate the vertical drop of particles. The separatorworks by not only slowing down the air but by changing its direction as well. Airflow entershorizontally and is immediately directed vertically downward by a target plate (Figure 1.14). Asthe air slows and moves downward, gravity takes over the large particles and drops them out ofthe airstream. Finer particles not affected by this will continue to flow in the airstream and exitthe separator.28 Fundamentals of Dust Collection Systems