An experimental study of fluidized-bed coating: influence of operating conditions on growth rate and mechanism

This study investigates the influence of fluidizing gas velocity, atomizing air, and liquid flow rates, liquid concentration, initial bed mass, and pa rticle size on the mechanism of growth of sand particles in a batch fluidiz ed-bed coater. An aqueous solution of NaCl was used as the coating liquid a nd sprayed in the bed by means of a pneumatic atomizer. The results showed that for a given particle size, the fluidizing air velocity was the most im portant factor affecting the coating kinetics and stability. The dominant m echanism was the onion-ring layering, especially at excess gas velocities h igher than 0.27 m/s. For a fixed value of the mass ratio of solute introduc ed in the bed to the initial particle mass, binder concentration, liquid fl ow rate, and the initial bed weight had no effect on the growth mechanism. The deposition quality was found to be affected by the droplet size. A decr ease of droplet size resulting from increasing the atomizing air flow rate permitted homogenous coating of the solid surface.