How can a pilot-plant trial help reduce risks when scaling up RMG granulation?
A pilot plant trial is a key intermediate step between laboratory and production, serving to secure the scale-up of a ring-layer granulation under conditions close to practice. It helps to identify critical process parameters, material behaviour and potential weak points at an early stage, before the process fails expensively or hazardously at full scale.
The most important contributions of a pilot plant trial include the following points.
Verifying the scalability of process parameters
At pilot scale, tool speed, chopper speed, fill level, liquid addition rate and spray conditions can be varied systematically. This establishes whether the settings determined in the laboratory also deliver stable, specification-compliant granulates at larger volumes.
Validating scale-up parameters
Dimensionless numbers such as the Froude number and the Newton number as well as the circumferential speed (tip speed) support the transfer of process conditions between laboratory, pilot and production scale. This reduces the risk of unexpected changes in particle size, density, flow behaviour or compressibility at large scale.
The Froude number relates to rotating free-fall, drum and throw mixers as well as to systems with a horizontally mounted mixing tool. In vertical mixers with forced restratification it is not a design or scale-up criterion. What is decisive there is that the mixing principle remains the same across all sizes and that the restratification covers the entire mixing chamber independently of the fill level; transferability is secured in the pilot plant with the original product.
Optimising liquid distribution and wetting
The pilot plant reveals whether the binder liquid is distributed evenly or whether over-wetting, lump formation or insufficient granule formation occur. Nozzle position, spray pressure and addition rate can then be adjusted accordingly.
Reliable determination of the process end point
Torque, power consumption or the temperature profile allow the appropriate granulation end point to be defined more precisely. This is decisive, since stopping too early or too late has a marked effect on granulate quality.
Assessing material behaviour and downstream processes
It becomes apparent how raw materials, binders and excipients react to shear, moisture addition and heat development, and how the resulting granulate quality affects downstream steps such as drying, sieving, tabletting or capsule filling.
Reducing material losses and development risks
Failed trials at production scale are cost-intensive. Pilot plant trials require less material and make it possible to identify and minimise risks before series production begins.
How amixon® scales ring-layer granulation (RMG) from laboratory to production scale
In the view of amixon®, the scale-up of ring-layer granulation (RMG) is fundamentally trial-based and cannot be represented by any reliable, purely computational scale-up method. Horizontally designed RMG granulators play only a secondary role here; the actual development focuses on mixing systems with vertically arranged mixing tool shafts.
Trial-based scale-up instead of a computational approach
In a ring-layer mixer-granulator, a product-specific equilibrium is established between granule build-up and granule destruction – governed by circumferential speed, residence time, liquid input and the granulability of the material. amixon® emphasises that pilot plant trials with the original product are necessary for this, because real volume flows can deviate from catalogue values and a purely computational scale-up would not be sound practice. From the trial data (particle size distribution, granulate stability, residence time, volume flow), the transition to the target size is extrapolated on the basis of experience.
Design constancy and the shifting of risk
Across all RMG sizes, essential design parameters remain constant: a round, machined mixing chamber with a defined tool-to-wall clearance, optionally temperature-controllable double walls, wear-resistant tools, integrated samplers and vibration-damping bearings on large machines. The scale-up risk is thus deliberately shifted into the documented pilot plant trial ahead of the investment – rather than into the commissioning phase of the production plant.
A focus on vertical mixing systems
Strategically, amixon® concentrates its development on vertical mixing systems such as single-shaft and twin-shaft mixers (VM, HM), conical mixers (AM) and mixer-dryer reactors (VMT, AMT) as well as further vertical designs (Gyraton® GM, EM, COM). These machines are manufactured in finely graduated sizes from pilot to large production scale and cover fill levels from approximately 10 to 100 % without compromising mixing quality.