(304c) Understanding Granular Behavior in Designing Solids Processing Equipments

Granular materials are widely used in industries such as power plant, cement, iron & steel, fertilizers, pharmaceutical, construction, mining and agricultural. Examples of granular materials are coal, sand, soil, gravel, sugar, salt, rice and tablets. Incline chute, conveyor belt and pneumatic systems are often used to transport the granular solids in industries. In industry, rotating cylinders, conical hoppers, silos and V-blenders are often used as solid mixing devices. Solid processing operations such as calcinations of limestone, reduction of iron oxide, clinkering of cementitious materials, cereal drying, calcinations of petroleum coke, and waste incineration are carried in the rotating cylinders. Rotating cylinders have certain advantages such as their ability to handle large variety of feed materials, provide long residence times and ease of cleaning. In spite of their versatile applications, the design of the solid processing equipments is ad hoc due to lack of understanding of internal processes. Moreover, one of the most interesting features of heterogeneous granular materials is their ability to de-mix or segregate under external agitation rather than to mix further. Hence, segregation causes problems in maintaining the uniformity of the bed materials and thereby affects the quality of final product. Though segregation is a common phenomenon in shear flow, vibration, shaking, and chute flow, yet understanding is incomplete. The scales - up is difficult due to the poor understanding of flow, mixing and segregation of granular materials in the solid processing equipments. Even the innovative way to improve the design of solid processing equipments is rare. In this study, experimental, numerical simulation and mathematical models are presented to understand the flow, mixing and segregation in granular materials and consequently to arrive at means to improve the design of the solid processing equipments. Scale -up rules are also discussed.