What do You Know About Fluid Bed Granulation Process?

1.What is fluid bed granulation?

A glimpse from fluid bed granulation process-picture courtesy: ThyssenKrupp uhde

Fluid bed granulation process is a technique to convert loose and dusty powder into solid granules for better usage. In this process, the powder is fluidized by blowing the air from below into the powder containing chamber. This air makes the powder move and float around making a fluidized bed of powder. Hence, the process is termed is fluidized bed granulation process.

The binder is sprayed over the fluidized powder particles which cause them to stick together and form granules. The use of steam or heated air to fluidize the powder particles allows a uniform and efficient mixing and drying of the ingredients.

2.What do you know about fluid bed granulation process?

The above image shows formation of granule in fluidized bed granulation process 

The fluid bed granulation process is a one pot procedure of making granules using fluidized bed granulator. This fluid bed granulation process comprises of the following main steps:

Powder feeding:

This is starting point of fluid bed granulation process. The mixture of powder which contains all the excipients and active ingredients is loaded from above head into the granulator which is product container of the fluid bed granulation process.

Before feeding the powder into the machine, it is ensured that the powder is blended well and there is uniform mixing of the ingredients. It is also recommended to ensure that there are free flowing powder particles for efficient fluidization. These qualities make a uniform powder bed for granulation.

Fluidization:

Fluidization of powder into granules-picture courtesy: research gate

This is the step which makes the powder particles act like a liquid, called fluidization. Once there is successful feeding of powder into the granulator, air is introduced into the granulator chamber. It is heated air which is blown from bottom of the granulator, already containing dry powder. The airflow is strong and exerts enough pressure on the powder particles to lift them and make them float in the chamber.

The drag force of the air flow becomes equal to the particles weight and powder particles float and move freely in the granulation chamber. These free floating powder particles just behave like a liquid and become fluid like. The have swirling and mixing movements without any are clumping.

This free mixing movement is essential so that the powder is properly mixed and prepared for binder spraying step. This fluidization of the powder particles evenly suspend and expose each and every powder particle to the binder which helps in effective granulation of the powder.

Binder atomization-Spraying :

Spray atomization phenomenon-picture courtesy: adobe

After the powder is fluidized and heated to the required temperature. This fluidized powder bed is sprayed with binder solution. The binder solution can be water or a sticky substance like starch or PVP. The spraying of binder is done through a nozzle attached in the granulation chamber. The spraying of binder through nozzle in form of fine liquid droplets is termed as binder atomization.

These liquid droplets come in contact with the fluidized powder particles. As soon as the powder particles contact the droplets, the liquid spread over the particles surface and bind them together in the form of agglomerates. As the binder is a sticky liquid it helps the powder particles to stick together upon contact.

The purpose of binder spraying is to make an initial contact among the powder particles to achieve the formation of granules.

Granule formation:

Granulation of coffee powder-picture courtesy: 123 RF

The binder wets the powder particles and makes them collide with each other and stick together. Over time, as more the liquid binder is being added, these small clumps start to grow in size and as more particles attach irregular shape granules start to form. This process is termed as nucleation and growth of granules. The size of the granules is controlled by operating system.

The binder spray and fluidization is well controlled. This ensures the growth of granules to a desired size. When the required binder spraying rate is achieved and there is required binder saturation of the particles, desired and properly formed granules are achieved.  This is the fluid bed granulation of powder. The granules thus achieved are of a uniform size.

Drying:

Drying-picture courtesy: vecteezy

Drying is the step which makes the freshly made granules solid and stable. While the granulation is being carried out, the hot air is consistently being circulated through the fluidized bed. This hot air evaporates any excess moisture from the binder and granules formed. This makes the granules dry out and become hardened.

Drying not only solidifies the granules but it makes them stable and strong. The result of drying provides us with free flowing granules.

Screening:

Separation of different particle size through sieving

Screening of the finally prepared and dried granules is done to ensure a uniform and required granular size.  This screening is done through specified size sieves which removes any oversized lumps as well as over fine granules or if there is any fine powder. This is important to ensure uniform size to improve the flow properties and compressibility of the granules.

3.Machine involved in fluid bed granulation process:

AIPAK multi-function fluid bed granulator

The following table will provide you with breakdown of major components inside fluid bed granulation process machine and the role of each part:

4.Different techniques of fluid bed granulation:

There are different techniques and variation of fluid bed granulator which you can find in different manufacturing industries. Let’s discuss the most commonly seen techniques of fluid bed granulators.

Top spray granulation:

This is the most widely used technique and often seen in manufacturing and processing industries. As the name suggest, it operates by spraying the binder solution from top of the granulation chamber. The hot air for fluidization is introduced from the bottom. It gives uniform granular size with good flow properties. They are common in pharmaceutical and food industry.

Bottoms spray granulation:

The atomizing nozzle is placed at the bottom of granulator chamber. The fluidized particles move upward under the influence of hot air and behave like an upward moving fountain of fluidized particles. The binder solution is sprayed from the bottom and particles are coated as they pass through the spray zone. They give precise coatings and used in controlled release or masked taste formulations.

Tangential spray granulation:

The binder spraying nozzle is attached at a tangential angle to the rotating fluidized powder bed. It creates a swirling liquid-particle interaction momentum. This system is integrated with rotary fluid bed systems.  They provide a better control over the structure and thickness of layer. This technique is used with larger size particles.

Rotor fluid bed granulation:

Rotor fluid bed granulation technique-picture courtesy: food feed fine chemicals

This fluid bed system has a rotating disc placed at the bottom of the granulator. The powder particles are fed into this rotating disc which creates a centrifugal force upon rotation and throws the particles outside in granulation chamber creating a spinning fluidized ring of the powder. The binder is sprayed at center or tangent angle colliding with swirling particles. It is used for granules with high mechanical strength and pelletization.

Multi fluid nozzle granulation:

This fluid bed granulation technique has a specialized nozzle which allows multiple fluids to mix. These different liquids can mix inside the nozzle or they mix as they came out of the nozzle creating a fine mist. This technique is used for complex formulations and takes less processing times with fewer steps.  It is used with fertilizers, sensitive chemical granules or combination tablets.

Continuous fluid bed granulation system:

Continuous fluid bed system-picture courtesy: food feed and fine chemicals

This fluid bed granulation system has a continuous operation of powder feeding, binder spray, drying and discharge. It is not like other fluid bed granulation techniques in term of batch systems. It has a nonstop and continuous operating system. They are best suited with high scale industries production and provide a consistent quality.

5.Applications of fluid bed granulation process:

6.Parameters that matters! (critical process parameters):

There are several critical parameters in fluid bed granulation process which must be monitored and carefully controlled. These parameters hold a significant importance because they directly affect the quality of granules produce through fluid bed granulation process.

These are the following parameters:

It should be kept in mind that all these parameters are interdependent. It means they are directly linked and dependent upon each other. The change in one parameter will exert a direct effect on the other parameter. Therefore, it is recommended to carefully optimize this parameter together in order to achieve successful and efficient granulation.

Conclusion:

Now you must have been well familiar with the fluid bed granulation process. The versatility, efficiency and advancement of fluid bed granulation process is widely adopted and extensively utilized in pharmaceutical industry, chemicals manufacturing, food processing industries and even agriculture. The combining of all the multiple stages of fluidization, atomization, granulation and drying in a single system make it a granulation favorite. To ensure production of fine quality granules, it is important that operator is well familiar and completely understands each stage. Each stage is equally important and has a significant role in maintaining process consistency. For more interesting information feel free to visit our AIPAK website.