Agglomeration Engineering Guide
Pharma powder technologies
Agglomeration / Size enlargement of solids particles
Powder, granules, tablets in pharma industries
A free online Engineering Guide to particles agglomeration and bulk solids processes in pharma industries
What is the agglomeration of solids particles ? How to agglomerate solids ? How to compact powders ? How to manufacture tablets ? Our Agglomeration Engineering Guide gives access to all knowledge interesting to Process Engineers in the field of bulk solids size enlargement to answer questions related to design or operations of agglomeration processes especially used in pharma industries.
⚙️ Roller Compactor Sizing & Throughput Calculator
Estimate production throughput, volumetric flow, linear specific roll force, and dynamic compaction pressure for dry granulation and pharmaceutical roll press sizing.
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Agglomeration of powders
Pharma solids particulates processes
Mechanisms of agglomeration
Agglomeration processes are ubiquitous in the process industry, be it wanted agglomeration through a process, or unwanted agglomeration like for example caking. This page is aiming at explaining what are the physical phenomena that cause agglomeration of powder particles, as such an understanding is critical to ensure that a factory is operating properly such processes as fluidized beds agglomerators, roller compactors, tablet presses, extrusion or sintering.
The Physics & Scaling of Roller Compaction
The total mass throughput \(Q\) of a roller compactor is mathematically governed by the volume of compacted ribbon passing through the minimum roll gap and its density:
\[ Q = \pi \cdot D \cdot W \cdot N \cdot S \cdot \rho_{ribbon} \cdot \eta_{eff} \]Where:
- \(D\) is the Roll Diameter
- \(W\) is the Roll Width
- \(N\) is the Roll Speed (RPM)
- \(S\) is the Roll Gap
- \(\rho_{ribbon}\) is the Compacted Ribbon Density
- \(\eta_{eff}\) is the Volumetric Feeding Efficiency
The specific linear force \(F_{linear}\) represents the primary scaling parameter to transfer powder blends between different pilot and manufacturing-scale roll presses:
\[ F_{linear} = \frac{F_{total}}{W} \]The estimated compaction pressure (average stress in the dynamic powder compression zone) is modeled as:
\[ P_{compaction} \approx \frac{F_{total}}{W \cdot \sqrt{D \cdot S}} \]Tabletting - Tablet presses
Tablet presses, and more generally rotary punch and die presses, are used in various industries to compact powder and granulates and then produce a tablet that can be easily handled, sold, and absorbed by the customer. Those machines are of course widespread in pharma industry and also now in the growing food supplement industries.
Compaction - Roller compactors
Roller presses are used to process bulk solids (powder, granules) in order to perform a dry granulation by compaction. This page is focusing on the design of roller presses, the mechanisms behind the agglomeration of the material which goes through a roller compactor, and the different applications of this technology.
💡 Practical Plant Engineering Rules & Sizing Constraints
- Nip Angle & Roll Slippage: For standard smooth rolls, the dynamic nip angle is restricted to 5° to 15°. If a material's friction coefficient is too low, the roll will slip, leading to severe fluidization in the feed chute.
- De-aeration Speed Limit: Exceeding a roll speed of 25–30 RPM in pharmaceutical processes typically causes severe fluidization, entrapping micro-bubbles in the dynamic ribbon that burst upon exit, leading to capping or splitting of granules.
- Roll Surface Selection: Use smooth rolls for highly cohesive, extremely fine pharmaceutical APIs to guarantee high-density ribbons. Fluted or pocketed rolls are preferred for free-flowing or slipping granules.
- ATEX Dust Safety: Dry pharmaceutical granulation areas must implement continuous monitoring and potential nitrogen purging. Granule sizing mills generate highly explosive fine dust classifications (ST-1/ST-2 class risks).
Frequently Asked Questions (FAQ) - Particle Agglomeration
What are the main mechanisms of particle agglomeration?
Particle agglomeration relies on several distinct physical forces: solid bridges (formed by crystallization, melting, or binders), capillary forces (due to liquid bridges), adhesive forces (electrostatic, van der Waals), and interlocking bonds. Understanding these helps engineers manipulate compaction speeds, feed pressures, and binder selections.
How do roll diameter and roll gap affect roller compactor throughput?
Throughput is directly proportional to both roll diameter and roll gap. Increasing the roll diameter allows a larger powder intake zone (larger nip angle), while a larger roll gap permits more volumetric flow but reduces overall ribbon compaction density if the compaction force is not proportionally raised. Optimization requires balancing both to prevent weak, friable granules.
What is specific roll force (linear force) in dry granulation?
Specific roll force is the total hydraulic force applied divided by the width of the compaction rolls, typically measured in kN/cm or lbf/in. It is the primary scale-up metric used to transfer formulations between laboratory-scale and commercial-scale roller compactors to maintain identical material ribbon density.