Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The counter-current gas fluidized cascade is a novel pneumatic device for the separation of mixed granular solids according to density and size difference. The study presented here is restricted to the application of the cascade in flotsam-rich binary solids systems.;The purpose of this study was to investigate the effect of the density difference and size distributions of the two solids, the height and speed of the paddles, the fluidization velocity and feed and product withdrawal rates on the separation performance of the cascade. It was observed that while a significant density difference would usually result in strong segregation in the simple fluidized bed, the cascade performance was less predictable. Separation efficiency appeared to deteriorate as the mean particle size of the components decreased. The present results indicate the importance of paddle height, paddle speed and fluidization velocity on separation efficiency. The experimental data was subjected to a multiple regression analysis. Additionally, a theoretical model was presented to describe the performance of the cascade under total reflux conditions. The dependence of diffusivity on the horizontal convective velocity of the fluidized solids was incorporated into the model. Agreement between the model and experimental results is reasonable.;Of the various solids systems investigated, the natural coal system is of industrial importance. The present study demonstrated the potential of the cascade as a simple and inexpensive device in coal beneficiation, despite the limitation on the purity of the product imposed by the degree of liberation of pyrite and ash from the coal matrix. Experiments with the natural coal system have also demonstrated that the separation effectiveness of the cascade could be improved by a multi-pass process in which the products and rejects were reprocessed in subsequent passes in the cascade.;The present work should be viewed as a first attempt to investigate the performance of the cascade in the separation of flotsam-rich solids systems. Continuation of the present experimental program as well as further theoretical development is recommended for a more thorough understanding of the cascade.



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