A Definitive Guide to Fluid Bed Granulation Process (Updated)

Fluid bed granulation is a popular material processing technique in many industries.

Quite a number of industries use it as a means of transforming the dusty powder into desirable granules.

But before I explore the fluid bed granulation process, let’s review granulation process in general.

What is Granulation?

According to an article published on an online resource center for the National Center for Biotechnology Information, granulation is the process of enlarging particles through agglomeration technique.

That is, the process of forming small particles into grains or granules.

This is a simple step-by-step illustration of fluid bed granulation process.

It is a technique that has been adopted in many material processing industries such as pharmaceutical, foodstuff and chemical industries just to mention a few.

For example, it is a common process in producing solid dosage drugs where it transforms formulations with improved compaction and flow characteristics.

Ideally, the process will ensure the final product has consistent hardness and uniform content.

As you can see in the image above, during granulation process, the particles adhere to each other.

This results in a final product with a large size as you can see in the image above.

Why Granulate Powder in Material Processing?

Normally, granulation forms an essential part of material processing due to the following key benefits

• Improves flow and compaction
• Enhanced compressibility in tablet manufacturing process
• Reduces dust during material processing
• Uniformly distributes essential ingredients within the granules

To achieve the desired quality of the final product, you need to choose an appropriate granulation technique.

Let’s have a quick overview of the various types of granulation processes.

Types of Granulation Processes

Generally, there are two types of granulation techniques and they include:

· Dry Granulation Technique

Dry granulation technique is the process of forming granules without the need for any liquid or solution.

It is a perfect choice for moisture sensitive materials.

This is a schematic diagram illustrating the dry granulation process. Image source: NIH

Ideally, it is the process of compacting and densifying powder to form granules.

There are many machines you can use in this process and a good example is the roller compactor for dry granulation.

Although this method is simple and cost effective, at times repeated compressing cycles may result in poor quality tablets.

· Wet Granulation Technique

In wet granulation technique, you’ll introduce a binder/liquid that causes aggregation of particles.

This process may seem a little technical, especially during the process of making a liquefied bed of material you intend to process.

Don’t worry, you’ll learn about all aspects of fluidization and fluid bed granulation in later in this article. It will be my main focus on here.

Before that, you need to note the following key aspects about wet granulation technique:

• Wet granulation requires the use of liquid, which is not the case for dry granulation technique
• Granulation liquid is a volatile solvent that is easy to remove by drying
• Should be non-toxic

The choice of liquid will depend on the type of material you intend to process.

For instance, you may opt for water, ethanol, isopropanol or any other aqueous solution.

So, I want you to remember that, the wet granulation technique is basically a fluid granulation.

Let’s review the core aspects of fluid bed granulation process:

The Working Principle of Fluid Bed Granulator

A study of fluidized bed granulation process shows that the process is generally the same irrespective of the machine design.

This is because the position of fluid bed spray system is always the same.

That is, you may opt for either a top spray granulation or side/tangential spray system.

In this section, you’ll learn about how a fluid bed process works.

But first, I want to review the overall design and structure of a wet granulation machine.

Design and Structure of Fluid Bed Granulator

Fluid bed granulation machines come in a wide range of shapes and designs depending on their functionality.

For instance, you may have a fluid bed granulator and coater or a fluid bed dryer and granulator.

In these two wet granulation machines, you will notice certain structural differences.

Here are two typical examples:

This is a technical drawing of a fluid bed dryer, granulator and coater.

This is a technical drawing of fluid bed dryer and granulator.

From these technical drawings, I am sure the structural difference in this fluid bed equipment is quite clear.

Apart from the structural design, as a fluid bed granulation manufacturer, we may include different intricate components to optimize operations.

That’s why it is important to mention these parts before we focus on the actual fluidize bed granulator principle of operation.

This is a simple side view of fluid beg granulation equipment. Image source: L.M. Collage of Pharmacy 

The table below shows part number and name:

Remember, the complexity of these machines will depend on the type of fluid bed technology.

For instance, in the multifunction fluid bed granulation machines, you may find one with:

• Top spray granulation
• Tangential spray granulation

In the next section, I will take you through the practical aspect of this process.

Later, you will learn about the fluid bed granulation parameters that you can control to ensure precise and quality material processing.

How a Fluid Bed Granulator Works

The working principle of fluid bed granulator machine is simple and straight forward. You can see this from the fluid bed equipment video below:

This video illustrates all the vital processes that take place in a fluid bed granulator and coater.

I’ll explain everything below to make it easy for you to understand:

As I mentioned earlier, the working principle of fluid bed processor tends to be the same.

For instance, a fluidized bed granulator and fluidized bed dryers, have nearly the same principle of operation.

But first, you need to ask yourself a simple question:

What is fluidization process?

Fluidization process is where a bed of particles in the product container is changed to a fluid state by an upward flow of liquid or gas.

The air moving upwards at high velocity blows the particles apart within the bed resulting in an “expanded bed”.

As the air flow increases, there reaches a point where the pressure drop in the bed system is equal to weight of the gas. At this point, we say the bed is fluidized.

Therefore, a fluidized bed refers to a phenomenon where solid particles are subjected to a specified amount of pressure that forces the particles to behave like a fluid.

This a fluidization process at different stages.

Now that you know what happens when a stream of gas flows into the bed, let me now focus on the fluidized granulator principle of operation.

Generally, the fluid bed granulation process involves three critical stages:

• Using a stream of air to fluidize the bed
• Adding a granulation fluid to agglomerate the particles
• Drying processed granules

Here is all you need to know:

· Fluidize the Wet Granulation Bed

Heat air to the required temperature and filter before directing it to the bed or product container of unmixed powders.

Depending on the fluid bed technology, the machine may be fitted with a fan or a pump.

Therefore, the fluid bed granulator can either blow or suck air into the product container.

By adjusting the airflow, it will reach a point where the bed particles will behave like a fluid. Thus, the bed is said to be fluidized.

Remember, fluidization is an efficient process of mixing particles. This granulation process is suitable for both heat sensitive and non-heat sensitive particles.

· Add Granulating Fluid

In most fluid bed granulation systems, the spray nozzle for granulating liquid is located at the top.

However, in systems that involve granulation and coating at the same time it is positioned on either side of the machine.

Now, with bed fully fluidized, the granulation fluid will be pumped from the reservoir to the spraying nozzle.

This is a fluid bed granulator with a top spray system.

As particles of powder collide against each other in the presence of granulation fluid, they adhere to each other forming granules.

Spray the granulation fluid continuously until the required size of granules form.

The system is fitted with exhaust filters. During the process, as air flows, some particles will tend to be blown away.

This exhaust filter traps the particles and it should be agitated periodically to release all trapped particles into the bed.

· Drying Granules

Drying is an important process in the fluid bed granulators.

With the right size of granules already formed the spraying nozzle is turned off.

The hot fluidizing air will continue to flow through the bed thereby drying all formed granules.

These are fully processed granules.

As you can see, the good thing about fluid bed granulation process is that, all processes take place within the same unit.

Therefore, you don’t have to worry about transferring dusty powder, high labor costs and time wastage.

However, you should know that this equipment is slightly expensive compared to dry granulation process.

It is for this reason that you have to optimize all parameters that may affect the operation of any wet granulation process.

This is why it’s vital to discuss the various fluid bed granulation process parameters.

Fluid Bed Granulation Process Parameters that May Affect Quality of Granules

As I said earlier, the ability to monitor various process parameters will ensure you get high quality granules.

This is one of the main reasons why as fluid bed equipment manufacturers, we insist on installing intelligent control systems that can monitor all fluid bed granulator variables.

Below are critical fluid bed granulation process parameters that you should monitor:

Formulation Variable in Fluid Bed Granulation

Here, you need to know the type and nature of materials you intend to granulate.

With this knowledge, you’ll definitely choose the right binder solution and other process parameters.

You can see particles moving within the fluid bed granulator and coater.

Basically, this is all you need to know:

• Properties of materials you intend to granulate

You need to analyze the following essential properties of material you intend to granulate: Density, shape/size, particle cohesiveness, degree of stickiness, wettability and static charges.

A good understanding of these properties will help you choose the right equipment for the fluid granulation process.

For instance, high static charges and cohesiveness make it difficult to fluidize the system.

• Properties of the binder solution

Choose a binder solution depending on the kind of material you intend to granulate.

There are a wide range of granulating solutions with varying friability, porosity, size distribution, bulk density and flow rate.

Furthermore, you need to consider the nature of the binder solvent too. Remember, different solvents have varying rates of evaporation.

Depending on the nature of the process at hand, you may choose either aqueous or organic solutions.

Apart from these, you need to review the fluid bed granulation technology.

That is, what are some of the key features that can improve efficiency of the material granulation process?

Fluid Bed Equipment Variables that Affect Efficiency of Material Granulation

I am sure at this point you’re conversant with the basic parts of a fluid bed granulation machine.

Here is a complete assembly of a fluid bed granulator and coater machine.

This is a fully assembled fluid bed granulator and coater.

So, here 5 vital aspects of fluid bed granulator equipment:

• Design of fluid bed equipment

There are many designs of fluid bed granulator equipment for different applications.

These include material granulation machines for R&D, laboratory or large pharmaceutical industries.

The position of the spraying nozzle may vary.

For instance, you may find a top spray mainly for granulation or side spray for both granulation and coating.

• Fluid bed equipment pressure

A pressure drop will affect the degree of material fluidization significantly.

It is the reason why you need to choose a machine with accurate and precise fan or blower.

Insufficient pressure will prolong the fluidization time and may not generate enough pressure for exhaust damper.

• Design and size of air distribution plate

This is a critical part for fluid bed granulating and coating machine with a side spray system.

You need to choose an air distribution plate with an appropriate open area since it affects the degree of pressure drop.

At times, it is advisable to have an overlap gill plate.

Apart from these, you have to choose a fluid bed granulation machine with a suitable shaker, blow back cycles, granulator bowl geometry and energy efficient motors.

I can advise you to go for a multifunction fluid bed granulation machine.

Variable in Fluid Bed Granulation Process

These are various parameters a fluid bed granulator technician can control as the machine operates.

Normally, adjusting these parameters directly affect the nature of the final product.

This image shows the spray process during fluid bed granulation process.

Let’s review some common fluid bed granulation process parameters that affect quality of the final product.

• Fluidizing air flow

A high airflow causes rapid evaporation, attrition and results in smaller granules. Choose the specified fluidizing air flow to prevent possible clogging.

• Inlet air temperature

We have two extreme cases here. Higher temperature results in fine granules, while lower temperature produces stronger and larger granules.

• Humidity level in the system

When there is an increase in the humidity, expect to dry the granules for a longer time. In most cases, this results in large granule size.

• Granulation solution/binder spray rate

Normally, fine droplet produces small granule sizes. In all fluid bed processors, the size of droplets depends on liquid flow rate, volume, atomizing air pressure and binder viscosity.

• Binder solution atomization pressure and volume

Always keep the mass to liquid ratio constant. This will help to maintain the size of granulating solution droplets constant and so are the granule sizes.

For instance, with pressure kept constant, enlarging orifice size will increase the droplet size.

Normally, liquid flowing at a high rate will produce larger granules and a reverse of this is true.

• Fluid bed spraying nozzle size and height

A suitable nozzle height is one that covers the entire surface of the bed. Normally, when it is too close, it will wet the bed hence producing large granules.

When the nozzle is too high, the granulation time will be longer and it will produce finer granules.

Quite a number of fluid bed manufacturers opt for binary nozzles that produce fine droplets.

I think with this critical analysis of the fluid bed granulation process parameters you can easily optimize the operation in any laboratory or pharmaceutical industry.

Conclusion

Fluid bed granulation plays a pivotal role in pharmaceutical material processing.

However, to maximize on ROI, you must consider all the vital aspects I have mentioned in this article.

That is, understand the principle of wet granulation and control variable parameters to suit the unique requirements of your applications.

I know this information can be overwhelming for a newbie in the fluid bed equipment industry.

That’s why SaintyCo team is always ready to help – contact us today.

References

• Studies on the Fluidised Bed Granulation Process – Source: De Montfort University Website
• study the Effect of Process Variables in Fluid Bed Granulation on the Physico-chemical Properties of Granules – Source: IJPSR Website
• Process Analysis of Fluidized Bed Granulation – Source: NCBI
• Fluid Bed Granulation Process – By G. Bedetti