Gas-solid Flow With Droplets And Granulation In A Spray Fluidized Bed

Spray fluidized bed granulation has been widely used in pharmaceutical,chemical,food and other fields.Fluidized granulation includes gas-solid two-phase flow,liquid evaporation and crystallization,and particle coating.The process of particle growth is affected by many parameters,such as fluidization,drying and material characteristics.In the process of spray granulation,it is necessary to organize well fluidization,and the key parameter to describe the granulation process is the growth rate of the particles.In this thesis,fluidization failure and the particle growth rate are investigated.The spray fluidized bed experimental system was set up,which includes the fluidized bed,spray system,gas system,measuring system and so on.By installing an internal central tube and strengthening air distribution in central area of the distributor,particles in the bed orderly circulate within the fluidized bed.A two fluid atomization nozzle is arranged within the central tube,and spray upwards,which enhances the contact between the droplets and the particles.The preheated fluidized gas controls the drying process.By turning on/off water spraying and heating experiment,it can be observed that the fluidized bed undergoes from the normal fluidization,to defluidization,and finally to the normal fluidization again.The results show that by increasing spray flow rate,the instability rate of the fluidized bed increased.Increasing the bed material weight and the particle size,the instability rate of the fluidized bed decreased.The variance of pressure fluctuation can effectively reflect the fluidization quality,and the variance becomes larger with the fluidization instability,and becomes smaller with the fluidization recovery.The occurrence of defluidization can be avoided by increasing the inlet temperature,spray pressure,or reducing the viscosity of the liquid.The ratio of liquid to bed materials weight is an important factor to determine the fluidization quality.It is helpful to maintain the stable coating process by controlling the ratio of liquid to bed materials weight.In the experiment of spray granulation,the particle coating process was revealed qualitatively by the dyeing liquid.In the process of coating,and the color of the particles is continuously deepened.In this paper,the growth mode of particles is a layer growth mode,and the increase of weight gain is almost linearly with time.The effects of particle size,flow rate,feed rate and binder concentration on the weight gain rate and growth rate of particle were investigated.The results showed that the particle growth rate was significantly increased by increasing of the feed rate.It is harmful to granulation if the fluidized air velocity is too small or too large.If the size of the bed material is smaller,the particles are more easily agglomerated.The particle growth rate increased with binder concentration.