The mechanism of the layering granulation is investigated in a top-spraying fluidized bed granulator(TSFBG). It's observed that there are instantaneous crystallization and deposition of sodium benzoate on granule surfaces in the layering granulation by scanning electron microscope (SEM). The granule growth rate of layering is affected mainly by the feed rate, the excess gas velocity and the spray droplets size, and slightly by the bed temperature. A new mathematical model to describe the heat and mass transfer process in TSFBG, composed of three algebraic equations, is proposed to predict the bed temperature profile, the temperature and the humidity of outlet fluidizing gas and the granules humidity in the granulator. The calculated results are in agreement with experimental values well.
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