Date of Award
Master of Science in Chemical Engineering - (M.S.)
Chemical Engineering, Chemistry and Environmental Science
Rajesh N. Dave
This study is directed at enhancing our understanding of the mechanism of dry coating and granulation in a rotating fluidized bed (RFB). The main objective was to study the feasibility of the coating and granulation processes using an REB, both quantitatively and qualitatively.
A force balance and kinetic model is applied to explain the coating phenomenon and also to investigate why coating takes place in certain particle material systems and not in others. An equation for the resultant velocity with which one particle collides with another has been suggested for the rotating fluidized bed coater. A condition, which predicts whether the colliding particles will stick together, has also been suggested. Experiments show that coating occurs with some host particles while it does not occur with others, in agreement with theoretical analysis.
It has been observed that Geldart Group C particles do not deagglomerate in the rotating fluidized bed. Thus it is assumed that they will collide with the host particle or with themselves to form larger agglomerates. However, experimental observations show a uniform and a fairly good quality of coating, which indicates that the agglomerated particles redistribute after sticking on to a host.
In the granulation studies, the method for binderless granulation using a conventional fluidized bed has been established. A rotating fluidized bed, in principle, operates on the same concept, except that during the forward gas flow, i.e., the fluidization phase, a higher gas throughput is achieved because of higher g due to the centrifugal force. This should result in better adherence between particles and formation of granules. The reverse flow rate will have no impact on the granulation since the reverse flow rate depends only on supply pressure but will aid in compaction. Hence, the strength of the agglomerate should be the same as that achieved with a conventional fluidized bed granulator using pressure swing.
Sawhney, Manish, "Feasibility study of rotating fluidized bed as a dry coater and granulater" (2000). Theses. 789.