| The mechanism of coating process in fluidized-bed spray granulation was analyzed theoretically firstly. The coating process can be divided into three stages-collision, extension and drying. There are two consequences after collision of droplets and fluidized particles, i.e. rebound or staying on the particles. As for those droplets capable of staying on the particles, they will not coat on the particles unless they extend. Through force analysis, an equation of whether the droplets will extend or not is studied. Subsequently, the coating process of potassium carbonate were studied in spray granulator .The study indicates that there is a lower critical operating temperature in fluidized-bed, besides, the higher fluid concentration and the lower fluidization velocity are, the faster the particles grow, but the operating temperature shows non-monotonous relationship with particles growth.It is useful that we study the parameters act on coating equable extent which is a very important factor effecting the granule's quality. With polyvinyl alcohol as film-forming materials and urea particle as seed particles, the influence on the coating equable extent of the fluidizing gas velocity, bed temperature, nozzle air pressure, solution concentration and gas distributor have been studied experimentally in a reverse conical fluidized bed. The results showed that the coating equable extent increased with increasing the nozzle air pressure. With increasing fluidizing gas velocity, bed temperature and solution concentration, the coating equable extent increased in the beginning phase and started to decrease when it got a max.On the basis of the experimental study, this paper presented a mathematical expression about coating equable extent by analyzing the transfer of mass and heat and the movement of particles in fluidized bed. It is as follows: By calculating experimental data, the results showed the theoretical value is approximately accord with experimental value.
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