Interpretation of fluidized bed granulator's concept of fluidization

       Interpretation of fluidized bed granulator's concept of fluidization

       Fluidized bed granulator is one of the equipment for the solid preparation production process generally used in the pharmaceutical industry. It is mainly used for the production of granules such as tablets, capsules, granules, etc. It is an ideal choice for granulation, powder mixing and drying processes. Widely used in pharmaceutical, food, chemical and other industries.

       The material is moved up and down in the hopper and the expansion chamber under the thrust of the airflow to form a fluidized state, but this state is not very regular and is not strictly controlled. The liquid is added to the system through a pneumatic nozzle (the height of which can be adjusted in several steps) installed in the expansion chamber. When granulating, the atomized liquid should cover the largest range of the material when it is fluidized, so as to obtain a concentrated particle distribution. During coating, the position of the nozzle should be adjusted to the area where the material moves most densely, so that the droplets can spread well on the particle surface and form a uniform film.

       In a device, the granular materials are stacked on the distribution plate. When the gas passes into the bed from the lower part of the device, as the air velocity increases to a certain degree, the solid particles produce a boiling state on the bed. This state is called fluidization. This bed is also called a fluidized bed. Adopting this method in addition to other technologies can complete the functions of material drying, granulation, mixing, coating and pulverization.

       Because of the different characteristics of solid particulate materials, and different factors such as the bed and air velocity, the bed can exist in three different forms.

       Let's take a look at its three stages:

       1. The first stage (fixed bed): When the fluid velocity is low, although the solid particles in the bed are in contact with the fluid, the corresponding position of the solid particles does not change. At this time, the state of the fixed particles is a fixed bed;

       2. The second stage (fluidized bed): When the fluid flow rate of the fixed bed stage gradually increases to a certain point, the solid particles will move to each other. If the fluid velocity is increased, the pressure loss in the bed will remain unchanged. Change, the solid particles will have irregular movement in the bed, and the bed is fluidized at this time;

       3. The third stage (airflow conveyance): When the fluid flow rate is greater than the sedimentation speed of the solid particles, the solid particles can no longer stay in the container and are taken out of the container by the airflow.

       For pharmaceutical industry applications, drying, granulating, mixing, coating, etc. are run in the second stage, and for pulverization, the second and third stages can be used for engineering operation.