(55g) Controlling Granular Segregation In Rotating Cylinders


The segregation of flowing granular materials is a commonly observed phenomenon in industrial processes and in nature. Segregation causes problems in maintaining uniformity of the processed material and leads to deviations in the quality of the final product. Granular materials are widely used in process industries, such as coal gasification, iron & steel, chemical, pharmaceutical, cement, food, detergents, mining, ceramic, and fertilizers. In order to design equipment such as rotary kilns, bins, silos, combustors, hoppers, chutes, hydro-cyclones, etc., in an effective and economical way, a thorough understanding of the various factors governing the flow characteristics of granular materials must be obtained. These needs have already motivated extensive analytical and experimental investigations of the flow of granular materials. Mixing, blending, heating, and granulation of these materials are frequently carried out in rotating cylinders or tumblers; however, when mixtures of two different types of particles are rotated in tumbler, they tend to segregate. Mixing and segregation in two-dimensional mixers depends on many factors including the type of components involved, the speed of rotation, the filling amount, and the mixer shape. All these parameters play an important role in the quality, degree, and the speed of segregation. We study the granular flow and segregation in rotating cylinders for different size and different density systems. We have found that periodic flow inversions of free-flowing materials may be used to effectively control both size and density segregation in free-surface flows. Parameters for the periodic flow inversion technique will be discussed. In a rotating cylinder, these inversions may be induced by placement of an axially located baffle within the flow. Flow induced granular mixing will be discussed. Segregation model will be presented.