Study On Coating Process In Fluidized-bed Spray Granulation

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 a taper fluidized-bed spray granulator and a cylinder fluidized-bed spray granulator respectively. The study indicates that there is a lower critical operating temperature in taper fluidized-bed than in cylinder 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.Based on the preceding study on mechanism of coating process, the ideal coating model was established. Due to neglecting the coating efficiency, there were differences between experimental and modeling values. Therefore, it is of vital importance to study coating efficiency. The coating process in fluidized-bed spray granulation is similar to queuing system, therefore, the coating process is simulated with queuing theory in Operations Research originally. Then, the equation of coating efficiency is set up. In order to validate the expression of coating efficiency, the operating factors including fluidized-bed temperature, concentration of fluid and fluidization velocity were studied. It shows that there are optimal operating temperature, concentration of fluid and fluidization velocity during coating process.