What are the most important criteria when selecting a vacuum mixing dryer for temperature-sensitive food supplements?
What is decisive is the product and the process objective: initial and target residual moisture, permissible product temperature, desired drying time, batch size and the behaviour of the product during drying. Vitamins, enzymes, plant extracts, flavourings and probiotic cultures differ in their sensitivity to heat, moisture, oxygen and mechanical stress.
Vacuum drying permits low product temperatures, because water or suitable solvents evaporate earlier at reduced pressure. What is decisive, however, is the interplay of vacuum, heating medium temperature, effective heat transfer area, product movement and evaporation rate. The lowest possible temperature is not always optimal if it increases the drying time and thus the overall thermal load.
The mixing tool must permit uniform product movement and heat transfer without unnecessarily damaging sensitive granulates, coatings or cultures. Particularly demanding are products that change during drying from a suspension or paste into a free-flowing powder. Vessel geometry, fill level, mixing intensity and flow behaviour determine how effectively the heated surfaces are used.
Important measured variables are product temperature, jacket temperature, pressure, speed and, where applicable, torque or the quantity of condensate. A moisture or water activity measurement can support end point determination. This must be validated reproducibly for the particular product.
Cleanability and residual discharge are particularly important with allergenic, highly active or strongly colouring ingredients. Machine geometry, surface quality, seals, discharge valve and accessibility must suit the intended cleaning procedure. CIP, WIP and manual cleaning must each be designed to suit the product and the plant.
Inert gas operation is worthwhile where ingredients are sensitive to oxidation or where it forms part of the explosion protection concept. It presupposes controlled oxygen limitation, gas-tight machines and measures against the risk of asphyxiation.
How amixon® selects the right vacuum mixer-dryer or conical reactor
What amixon® provides in addition
amixon® supplies not merely a vacuum mixer-dryer but develops the appropriate process solution on the basis of the actual product behaviour. The focus is not on target temperature and residual moisture alone but also on changing consistencies, heat transfer at real fill levels, product protection, residual discharge and cleanability.
One apparatus for several steps
The AMT and VMT vacuum mixer-dryers and reactors can – depending on the version – combine mixing, temperature control, vacuum drying, de-agglomeration and reacting in a single closed apparatus. They process dry, moist, pasty and suspended products, even where the consistency changes considerably during drying. Product transfers, interfaces and potential contamination risks can thus be reduced.
The three-dimensional product movement is generated at comparatively low circumferential speeds. This supports uniform temperature distribution and effective heat transfer without placing unnecessary mechanical stress on sensitive constituents. Where required, a cutting rotor can be used in a targeted way to break up tough plastic phases or agglomerates and to stabilise the course of drying.
AMT: flexible and readily dischargeable
The AMT conical mixer-dryer is particularly advantageous where batch sizes vary widely, where products change frequently or where high-value products are to be discharged almost completely. The conical geometry guides free-flowing product to the central outlet; with the ComDisc® discharge system, residual discharge of up to 99.997 % is possible with suitable products.
The AMT thus offers an economical combination of a wide fill level range, product-protecting movement and low product loss. This is relevant in particular for high-priced vitamins, extracts or formulations with allergenic constituents.
VMT: widening the process window
The VMT flat-bottom vacuum mixer-dryer is suitable for demanding drying and reaction tasks where high mixing quality, effective heat transfer and a wide range of consistencies come together. The vertical helical mixing tool moves the product three-dimensionally and can support homogeneous product movement even at low fill levels.
The machines can be built gas-tight and can be operated in the pilot plant under vacuum down to below 5 mbar absolute as well as under overpressure. Temperature ranges from −70 to +350 °C and pressures up to 30 bar are available for trials. Demanding processes involving vacuum, inerting, temperature changes or reaction steps can thus be investigated realistically.
Trials instead of assumptions
The particular strength of amixon® is testing close to the process with the original product before the investment. In the pilot plant, residual moisture, heat transfer, product movement, homogeneity, product protection, residual discharge and cleanability are investigated under realistic operating conditions.