Pharmaceutical Wet Granulation Line Complete Guide - Powder to Ready-to-Press Granules
- Marketing @ STV Machine
- May 29
- 9 min read
Updated: 3 days ago
Every tablet starts as a powder. But raw powder alone cannot be compressed directly into a reliable, consistent tablet. It does not flow well enough to fill a tablet press die uniformly. It does not compress predictably. And without the right preparation, the active ingredient may not be distributed evenly across the batch, which means tablets in the same batch could contain different doses.
Granulation solves all of these problems. It is the process of transforming fine, difficult-to-handle powder into larger, denser, more uniform granules that behave predictably at every step that follows. The granulation line is the sequence of machines that makes this transformation happen: from incoming raw material to a blend that is ready for the tablet press.
Granulation does not just prepare powder for compression. It builds the consistency that every downstream step depends on.
This blog walks through the complete wet granulation line step by step in simple clear way (no engineering or pharmaceutical experience required to understand). It covers what each machine does, why the step exists, and how it connects to the next. Each step is covered as an overview. For those who want to go deeper on any individual machine or process, dedicated blogs on each topic are available on the STV Machine website.
Wet Granulation and Dry Granulation — A Brief Note
There are two main approaches to granulation in pharmaceutical manufacturing. Wet granulation uses a liquid binder to agglomerate the powder. It is the most widely used method for oral solid dosage forms because it produces granules with excellent flow, compressibility, and content uniformity, narrowing particle size distribution, eliminating segregation, and ensuring superior compressibility compared to unprocessed powder blends (Pharmaceutical Technology, 2025).
The lesser used technique, Dry granulation, uses mechanical force to compact the powder without any liquid suited to moisture-sensitive or heat-sensitive active ingredients. Both are valid approaches, but the granulation line described in this blog refers to wet granulation throughout.
Step 1: Powder and Pre-Treatment
The granulation process begins with the raw materials: the active pharmaceutical ingredient which comprises the medicine its self and the excipients, which are the supporting materials that give the tablet its structure, help it dissolve, and make it manufacturable. These arrive from suppliers as fine powders, measured and checked against specifications before entering the line.
The condition of the incoming powder matters more than many manufacturers initially expect. Particle size, moisture content, and bulk density all affect how the powder behaves in the granulator. Powders that arrive with the right characteristics can go directly into the High-Shear Mixer Granulator. Those that arrive with lumps, oversized particles, or inconsistent particle size need pre-treatment first.
Lumps in raw powder most commonly form during storage or transport. Pressure, humidity, and temperature changes cause powder particles to compact and bond together. When lumpy material enters the granulator without preparation, the mixing and binder distribution across the batch becomes uneven from the very first moment. The pre-treatment step removes this variable before it can affect the rest of the line.
The STV Fitz Mill FM-200 addresses this by using high-speed rotating blades working against a perforated screen to break material down to a consistent particle size. The screen controls the maximum size of material that passes through, so the output is uniform regardless of the condition of the incoming material. Hammer mills of this type work in two stages: particles are first impacted by the rotating blades, then forced through the screen, with the screen size determining the final particle size ceiling (PMC, 2020). Blade speed is variable and the blades are reversible, making the machine adaptable to different material types and hardness.
For manufacturers whose raw material challenge is not hard lumps but oversized granules or agglomerated powder that needs gentle breaking down and sizing simultaneously, an alternative pre-treatment option is the STV Sieving Granulator SG-250.
The SG-250 combines sieving and granulating in a single pass. Material is fed through a rotating cylindrical screen that breaks up soft agglomerates and oversized particles through gentle mechanical action while simultaneously classifying them by size. What passes through is a powder that is both de-agglomerated and within the target particle size range, ready for the granulator.
The choice between the FM-200 and the SG-250 comes down to the nature of the incoming material. The FM-200 is the right tool for harder, denser lumps that need impact force to crush and reduce. The SG-250 is better suited to softer or more fragile materials where aggressive milling would produce too many fines, because its strength is precision sizing rather than crushing. Both deliver the same outcome: a consistent, well-characterised starting material that gives the High-Shear Mixer Granulator the best possible conditions to build a uniform granule.
It is also worth noting that the SG-250 is not limited to pre-treatment. The same machine can be used later in the line for dry sieving after the Fluid Bed Dryer, making it a flexible piece of equipment that can serve two steps depending on how the line is configured. This is covered further in Step 4.
Whichever the machine FM-200 or the SG-250, the output of this step is a consistent, well-characterised starting material. This gives the High-Shear Mixer Granulator the most uniform input conditions possible, which is where the granule itself is built.
Step 2: Building the Granule with a High-Shear Mixer Granulator
This is where granulation actually happens. Pre-treated powder and excipients are loaded into the High-Shear Mixer Granulator bowl. A binder liquid such as water, an aqueous binder solution, or a solvent is added and sprayed into the powder mass. The agitator and chopper work together to distribute the binder and agglomerate the powder into wet granules.
The STV High-Shear Mixer Granulator (HMG Series) uses a Z-shaped agitator with three mixing blades arranged at 120-degree intervals. The gap between the blade tip and the bowl base is kept between 0.7 and 1.2mm, narrow enough that every part of the batch passes through the high-shear zone, leaving no dead spots where unmixed powder can accumulate. The multi-blade chopper breaks up large agglomerates as they form, maintaining a consistent granule size throughout the run.
The end point of granulation, when the moment when the granule has reached its target structure, is detected by torque measurement. As the granule mass develops and becomes denser, the resistance on the agitator motor increases. A graphical trend on the control panel displays this torque in real time. When the reading stabilises at the target value, granulation is complete. Published research confirms that granule end-point can be reliably determined by correlating torque profile data with target particle size, with the plateau phase of the torque curve indicating that granule growth has reached the desired range (Dan et al., 2023). This approach removes the subjectivity from the process end point, giving consistent results batch after batch. Some machines rely on manual observation and operator judgement to determine the end point, STV Machine uses torque measurement as a more objective and reproducible method.
The granule structure set in this machine, size, density, particle size distribution, and porosity, is what every subsequent step in the line works with. This is covered in depth in our dedicated blog on the High-Shear Mixer Granulator and Fluid Bed Dryer.
Step 3: Drying and Setting the Granule with a Fluid Bed Dryer
Wet granules from the High-Shear Mixer Granulator contain the moisture that was added during granulation. Before they can be compressed into tablets, that moisture must be removed precisely, uniformly, and down to a specific target moisture content. Too much moisture and the granules will not compress properly. Too little and they may become brittle. The Fluid Bed Dryer handles this step.
Conventional fluid bed dryers often use vertical upward airflow through a perforated plate to dry the granules. Airflow While this may be functional, effectivity might be decreased due to granule clumping and air channeling, reducing overall granule uniformity. Check this article written comparing conventional FBD and STV Machine's FBD: article
Heated air enters the STV SD(GC) Fluid Bed Dryer through the Bottom Plate STV Disk Jet at the base of the chamber. The angled vanes of the Disk Jet plate give the airflow a tangential direction, creating a cyclonic movement that lifts and rotates the entire granule bed continuously throughout the drying run. Every granule stays in motion. Every granule is exposed to the heated airflow for the same amount of time. The result is a batch with uniform moisture content from top to bottom and beginning to end.
The SD(GC) Series is also capable of spray granulation and pellet coating — additional processes that use the same chamber and the same Bottom Plate STV Disk Jet technology. For this blog, the focus is on its role in the granulation line: drying the wet granules produced by the High-Shear Mixer Granulator. A full explanation of the SD(GC) technology and the STV Disk Jet airflow is available in our dedicated blog on fluid bed drying.
Step 4: Consistent Granules Through Dry Sieving
After drying, granules are discharged from the Fluid Bed Dryer and passed through the STV Lifting Device LT(R) Series — a dry sieving machine whose lifting mechanism is what allows it to connect directly to the FBD discharge and feed the sieved granules into the IBC below. The purpose of this machine is always sieving. The lifting is simply the engineering that makes the inline sieving possible without manual transfer between vessels.
Dry sieving does two things for the batch. First, it breaks up agglomerates and granules that clumped together during drying as moisture evaporated and surfaces made contact. Second, it classifies the granule mass by size, allowing particles within the target range to pass and retaining those that are too large. The result is a granule batch with a consistent and narrow particle size distribution, the quality characteristic that most directly determines how evenly the material will compress in the tablet press.
This is the last quality gate before the granule blend is prepared for compression. The granules that pass through the dry sieve are the granules that go into the final blender, then ultimately into the tablet press.
Step 5: Final Blending
Dried, sieved granules are transferred into the final blending step. At this stage, the remaining excipients that could not be added during granulation, such as primarily lubricants like magnesium stearate, are added to the granule mass. Magnesium stearate is the most widely used boundary lubricant in tablet manufacturing: it forms a thin layer on the granule surface that reduces friction between granules and the tablet press die, enabling smooth tablet ejection (Hanada et al., 2020). These need to be blended in gently and homogeneously: too little blending and the lubricant is not evenly distributed; too much and the granule surface becomes over-lubricated, which can slow disintegration and reduce tablet tensile strength (Saniocki et al., 2014).
The STV IBC Lift Blender LB Series handles this step. The granule mass and lubricants are loaded into an Intermediate Bulk Container (IBC). The LB Series lifts the IBC and rotates it at variable speed, tumbling the contents until the blend is uniform. Because the material stays inside the container throughout blending, there is no transfer between vessels, no exposure to the environment, and no loss of material at this stage.
What comes out of the IBC Blender is the final granule blend that is homogeneously mixed, consistently sized, and at the right moisture content. This is the finished output of the granulation line. It is ready for the tablet press.
The Line as a System, Why Each Step Depends on the One Before It
What the step-by-step walkthrough above describes is not just a sequence of machines — it is a system. Each step in the granulation line produces an output that becomes the input for the next. The quality delivered at one stage determines what the following stage has to work with.
Raw powder that is not properly pre-treated puts uneven material into the granulator. A granulator that produces a wide particle size distribution puts inconsistent granules into the dryer. A dryer that dries unevenly puts granules with variable moisture into the sieve. A sieve that passes material outside the target range puts an inconsistent blend into the final blender. And the tablet press receives whatever the blender produces.
Each machine in the granulation line inherits the quality or the problems of the step that came before it. The line is only as consistent as its weakest step.
This is why STV Machine designs the granulation line as an integrated system. The HMG Series, SD(GC) Fluid Bed Dryer, Lifting Device, and IBC Lift Blender are engineered to hand off cleanly from one step to the next. Each machine is sized and specified relative to the others, so the output of one is matched to the input requirements of the next.
For manufacturers who are building a new granulation line, evaluating their current setup, or looking to understand where quality problems in their tablets are originating, the granulation line is the right place to start.
Learn More or See the Line in Action
The granulation line described in this blog is built and supported by STV Machine, a manufacturer of pharmaceutical processing equipment with production facilities in Ho Chi Minh City, Vietnam.
Each step of the line covered in this blog has a dedicated article on the STV Machine website for those who want to go deeper on any individual machine or process.
To learn more about the granulation line, contact STV Machine directly:
• Email: sales@stvmachine.com.vn
• LinkedIn: linkedin.com/company/stvmachine
• Website: www.stvmachine.com.vn
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