Agglomeration of Particle Systems in Fluidized Beds

Work performed on agglomeration of particle systems in fluidized beds at both low temperatures (granulation) and high temperatures (sintaring) is described in Part I and Part II of this report, respectively.

Part I

Part I includes a detailed review of the available literature on low temperature granulation as well as a description of original work performed on the behaviour of liquid bridges between two relatively moving particles. Experimental results are given for bridge strength measurements using two small spheres in a vibrational motion. These results are then compared to a modified form of a theoretical model developed from the well-known lubrication approximation. From both, the reviewed literature as well as from the experimental and theoretical work performed on moving liquid bridges, it is clearly concluded that the fluid (binder) viscosity and its rate of change with time are two of the most important binder characteristics which ultimately determine agglomerate growth in a granulator. It is also concluded that the instrument at CCNY used to measure bridge strength as a function of particle velocity (frequency, amplitude) and binder viscosity may be an efficient tool to characterize industrial binders. Based on these findings, future work is proposed to actually correlate bridge strength measurements with agglomerate growth rates in an experimental granulator.

Part II

Part II of the report includes the description of a large number of dilatometer and defluidization experiments performed at high temperatures with a great variety of amorphous and crystalline materials. Sometimes these experiments were complemented by differential scanning calorimeter (DSC) experiments to determine characteristic temperatures of recrystallization and/or phase change. The defluidization experiments were performed on the newly constructed fluidized bed agglomerator capable of operating at temperatures up to about 1150°C. Among the materials characterized during these experiments were different polymers and glass powders, sodium chloride, sodium bromide, sodium citrate and ferrous chloride crystals and a large number of more complex materials such as a titanium dioxide ore, FCC catalyst and fly ash samples. It was clearly established that the minimum sintering temperature (and other phase transition temperatures) can be determined using dilatometry. It was also shown that fluid bed defluidization (high temperature agglomeration) always occurs at temperatures somewhat higher than the minimum sintering measured in the dilatometer. Furthermore, the behaviour of the powder during high temperature fluidization can be reliably determined from the dilatometer experiments. Future work on this project will include upgrading both the dilatometer and the fluid bed agglomerator to withstand temperatures as high as 1500°C. The new dilatometer will also enable tests to be performed under a controlled atmosphere thereby allowing study of agglomeration due to chemical reactions.