Granulation Process In A Vibrated Fluidized Bed Spray Granulator

Granulating technique has been applied widely in many industries. The vibrated fluidized bed granulation will effectively overcome these disadvantages of wide distribution of particle size and high dissipation of energy, existing in the traditional fluidized bed and the spout-fluidized bed. The granulation technique in VFB is especially suitable for the medium and small scales process of layering granulation. Accordingly, investigating the granulation characteristics in VFB, developing new practical technique of granulation for the producing process have important scientific value and extensive application prospect.In this paper, urea particles and oil-vegetable seeds as initial particles are used to study granulation process in a vibrated fluidized bed, where the initial particles grow in a layered manner by spraying melt Urea solution on them and reached the required granule size. The coating efficiency and the particle's size are measured under various experimental conditions. The effects of particle type, liquid spraying rate, liquid concentration, fluidizing gas velocity, vibrated intensity, nozzle position and atomization air pressure on the growth of particles have been analyzed and discussed. The experimental results show that at fluidizing gas velocity u=1.86umf, the oil-vegetable seeds get higher growth rate than the urea particles. Higher liquid spraying rate and higher urea solution concentration, lower nozzle position are preferred conditions for the growth of particles. However,liquid spraying rate should be limited to less than 8.5kg/h for u= 1.5-2.0 umf. On the premise that the particles were fluidized normally, lower gas velocity is fit for the particles growth. Gas velocity should be ranged from 1.5 to 2.0umf. Appropriate vibrated intensity is a preferred condition for the growth of particles, which can reduce gas velocity greatly, and deal with the crushing and the conglomeration of particles effectively. But the particles growth rate is decreased along with the overage vibrated intensity, should be ranged from 1 to 2.A mathematical model for the particles layering growth is developed based on the mechanism of layering growth and law of conservation of mass. A formula for calculating the particle diameter was also deduced. Comparing the predicated values with the experimental values, the results show that the deviation between them is ± 8.8%. Therefore the precision of the model is proved .