Analysis of Process Factors in Granulating Mechanism of Fluidized Bed

Fluidized bed granulator Analysis of process factors during granulation

Fluidized bed granulation is also called one-step granulation, which is a method of mixing, granulating and drying conventional wet granulation in one step in a closed container. In recent years, due to the GMP certification faced by the pharmaceutical industry, fluidized beds have been widely used in pharmaceutical factories in China. The principle of fluidized bed granulation is that in a fluidized bed granulator, compressed air and a binder solution are atomized by a nozzle at a certain ratio and sprayed onto a fluidized material powder on a fluidized bed.

First, the droplets make the contacted powder wet and coalesce around them to form a particle core. At the same time, the droplets that continue to be sprayed on the surface of the particle core create a bridging effect, so that the particle core and the particle core are in between. Particle cores and particles combine with each other to gradually form larger particles. After drying, the liquid bridge between the powders becomes a solid bridge, and round porous particles are obtained.

Because the whole process of fluidized bed granulation is not affected by external forces, it is only affected by the air flow in the bed. Therefore, the granules produced are small in density and low in strength, but the granules have uniform particle size, good fluidity and good compression formability.

The influence of technological factors on granulation of fluidized bed granulation mechanism:

1. Inlet temperature

Inlet temperature should be controlled in an appropriate range. If the solvent of the binder is water during granulation, according to the nature of the material and the required particle size, the feed temperature is generally set within the range of 25-55 ° C. It has been experimentally proven that when the inlet temperature is increased from 25 ° C to 55 for the same material At ℃, the particle size of the obtained particles decreased from 450 um to 240 um.

If the solvent of the adhesive is an organic solvent such as ethanol, the inlet temperature should be slightly lower, generally in the range of 25-40 ° C.

The temperature is too low, the solvent cannot be swept away in time and the powder is excessively wetted. Part of the material powder will adhere to the wall of the device and cannot be fluidized, which easily causes particle adhesion and agglomeration.

The temperature is too high and the intake air temperature is too high, which can cause the adhesive liquid droplets to be dried prematurely and fail to effectively granulate, and may also cause changes in the properties of some temperature-sensitive materials.

When drying, the inlet temperature is generally set to about 60 ° C.

If the temperature is too high, the solvent on the surface of the particles will evaporate too fast, which will prevent the inner layer of solvent from spreading outwards. As a result, a large number of dry and wet particles will be produced.

If the temperature is too low and the drying time is too long, a lot of fine powder will be produced.

2. Fluidized air volume

The fluidizing air volume refers to the amount of air entering the container, which should be at a value that makes the material ideally fluidized.

When spraying granulation, if the air volume is appropriate, the material is in a good fluidized state, and the heat exchange is in a balanced state, which is conducive to granulation.

If the air volume is too large, the moisture of the adhesive will evaporate too fast, and the adhesive force will be weakened. At the same time, the adhesive droplets will not be able to make full contact with the material, so that the particle size distribution is wide and there are many fine powders. When the air volume is too low, The solvent cannot be swept away in time, and the fine powder of the material is excessively stuck. If the air volume is not increased in time, large particles with large particle sizes will appear, and then a large mass will be formed, causing a collapsed bed. This is very serious in industrial production. Accident.

粒 During the granulation process, sometimes a lot of powder is adsorbed on the filter bag, which causes the actual fluidized air volume to decrease. The fluidized air volume should be appropriately increased.

3. Atomizing air pressure

The role of atomizing air is to make the adhesive solution form droplets. The particle size of the droplets is directly related to the particle size of the particles obtained. The greater the pressure of the atomizing air, the smaller and more uniform the particle size of the resulting droplets. The smaller the particle size of the obtained particles.

When the spray pressure is too low, the atomized droplets increase, the spray cone angle of the atomized droplets decreases, and the range of wetted particles is reduced, resulting in uneven distribution of the atomized droplets, and it is easy to generate large wet masses in local areas. .

Because the fluidized state of the material will be affected by the dual effects of fluidized air and atomized air, the pressure of the atomized air will also have a greater impact on the fluidized state of the material. When the pressure of the atomized air is increased, the material flow The fluidized state will weaken, and the fluidized air volume should be increased; otherwise, it should be considered in operation.

4. Adhesive flow rate

The flow rate of the adhesive and the temperature of the inlet air determine the humidity in the granulator. When the inlet temperature is constant, increase the flow rate of the adhesive, the particle size of the droplets of the adhesive, and the humidity in the granulator. Both of them increase, and the wet particles cannot be dried and agglomerated in time, which may cause collapse.

Under the same conditions, when the flow rate of the binder is too low, the particle size is smaller and the fine powder is more, which not only prolongs the operation time, but also easily blocks the nozzle. If necessary, the flow rate should be controlled according to the viscosity of the adhesive solution. If the viscosity of the adhesive is too large, the flow rate of the adhesive can be appropriately reduced, but the inlet temperature should be increased, otherwise it will easily cause nozzle blockage and collapse. When the viscosity of the adhesive is low, the flow rate should be higher.