A theoretical study with experimental support on granulation process of NaCl and $Na_2SO_4$ were carried out in a 0.1 m diameter of glass-walled fluidized-bed granulator.
In the batch fluidized-bed granulation experiments, operating ranges which allowed growth mechanism as a coating mode were obtained and the corresponding results were utilized in a steady state fluidized-bed granulation experiment. Among many materials, NaCl and $Na_2SO_4$ were chosen for segregation as well as granulation experiments.
A model was proposed to predict the particle size distribution and growing rate of particle in an unsteady state fluidized-bed granulator. Particles in the bed were grown by a spraying of solution as they were dissolved in the bed.
Simulation study showed that particle size distribution of bed is influenced by the initial particle size in the fluidized bed and its distribution is broadened as time elapsed. and the experimental results showed that this model could predict growing rate well. Operating conditions for governing layered growth were observed in the fluidized bed granulators. These were established by variable studies on fluidizing gas velocity, spray solution concentration and flow rate, air to liquid volume flow ratio (NAR ratio) and temperature of the bed.
A high degree of segregation was confirmed to be achieved at the limited range of the fluidization condition in the boot and of the particle size in the main fluidized bed. Particles containing 3 cut size were used preliminarily to study about minimum fluidization velocity and to understand segregation phenomena.
Segregation effect were observed extensively in the a segregation boot with the particles containing 7 cut size. Segregation air flow rate and size distribution effects were studied in a 10 cm diameter cold bed fluidized reactor. the empirical segregation factors obtained in this study were in good agreement it experimental observation.
Pressure fluctuation was also observed. The effect of particle size, relative gas velocity and the amount of the bed on the mean pressure drop and pressure amplitude were determined. The experimental results showed that the pressure fluctuation signal seemed to be a valuable tool to analyze the bed conditions such as changes of bed height and mean particle size in the bed during the fluidized bed granulation.
A mathematical model was developed to predict the particle size distribution in a steady state fluidized bed granulator with selective withdrawal of large particles and was confirmed through a series of experiments. The simulation study showed that as the seed particle input flow rate increases, the average particle size of bed material and output flow rate of grown material decreases. It was also demonstrated that the simulation results were in good agreement with the experimental results in a 10cm diameter steady state continuous fluidized bed granulator.
