Air classification — Part I, Equipment and selection
Air classification uses a stream of air to separate particulate material into a coarse fraction and a fine fraction. Classification is generally by particle size, although shape and density characteristics can also play a role. Strictly speaking, classification can be done in any gas, but air is used in the majority of cases because it is free and readily available. However, gases such as nitrogen or flue gas are advantageous under special conditions particularly if the solid material is highly explosive.
Part I of this article, the first of two, provides updated and revised information on the types of air classifiers available today. Since the author's last review of this topic, some classifier types have been discontinued while new ones have been put on the market. Parameters of equipment selection are also discussed. In the September issue, Part II will focus on developments and insights in the field of air classification obtained during the author's R& D and plant work. Formulas for measuring air classifier performance will be presented and particle and rotor dynamics will be discussed.