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Controlled conditions

Production of agglomerate-free and highly concentrated dispersions

When large quantities of powders such as starches, hydrocolloids, emulsifiers or stabilizers are to be mixed or dispersed into liquids, for example for subsequent spray drying as an emulsion or suspension, the same question often arises: How can the raw materials be processed efficiently and hygienically to form a reproducible, homogeneous and stable dispersion without the typical problems such as dust formation, insufficient wetting, formation of agglomerates and the associated fluctuations in quality?

ystral Conti-TDS In the Conti-TDS, liquid and powder enter the wetting zone via separate paths

Powders have a very large specific surface area, which can be several thousand square meters per kilogram. If the powders are poured onto a liquid surface of only a few square meters, an enormous disproportion of liquid to powder surface is created - apart from the dust load. Depending on the properties of the powders, the liquid penetrates more or less into the fill and only wets it incompletely.
only partially. The powders remain on the liquid surface and can only be incorporated by generating strong turbulence, for example by forming a tumbler, and the associated air entrainment.
Agglomerates are often formed which, depending on the powder, are surrounded and protected by a flexible shell that is already wetted at the beginning. These agglomerates can only be destroyed later on with increased energy and time expenditure.

Loss-free suction directly from the hopper
In addition to the dust pollution and agglomerate formation that occurs with this method of working, more material is often used to produce the desired effect than would be necessary for complete wetting due to inefficient utilization of raw materials. Some of the raw materials "disappear" as dust in operating equipment, suction devices and filters. Powders that tend to stick encrust on the container wall and on built-in parts such as the agitator shaft. Product quality suffers and can vary from batch to batch.

The Conti-TDS powder wetting and dispersing machine from ystral, Ballrechten-Dottingen, which operates according to the rotor/stator principle, differs from all other systems on the market. It allows powders to be sucked into liquids directly from a bag, hopper, container, big bag or silo, wetting and dispersing them in a matter of seconds without any dust or loss. It is installed outside the container, not inside it, and connected to it via pipes or hoses. Similar to a pump, the machine circulates the liquid in the container. The special geometry of the rotor creates a vacuum inside the dispersion chamber through which the liquid flows. With this vacuum, powders can be sucked in directly from the container in a dense flow without dust or loss.

Dispersing with high shear energy
The liquid flow is dispersed in the dispersion chamber with high shear energy, which greatly increases the surface area of the liquid into which the powder is sucked. The vacuum inside the dispersing chamber causes the air contained in the powder flow to expand and the distance between the particles increases. The two material flows (liquid and powder) enter the dispersion chamber via completely separate paths and are only brought together in the dispersion zone at defined shear gradients. This creates ideal conditions for wetting the individual particles. This process enables fine distribution at the moment of wetting and often ensures significantly better product properties compared to conventional powder application.

Depending on the recipe, several different raw materials can be dispersed consecutively and fully automatically, whereby the extraction can take place from different containers. Until the recipe quantity of powder is reached, the liquid is conveyed in circulation and concentrated with solids (maltodextrin, Gunmli Arabictm1). After the solids have been fed in, further dispersion and homogenization can take place in the circulation at a high feed rate with the powder inlet closed until the required particle size distribution is achieved or a dissolving process is completed. The oil phase can then be sucked into the agglomerate-free solution or suspension and emulsified. The high unrolling performance and the fine distribution in the vacuum suction area of the machine result in a very fine, homogeneous and stable emulsion, which in most cases eliminates the need for genisators. If reworking is required, the quality of the emulsion significantly reduces the reworking time.

During the dispersing and wetting process, the micro air bubbles adhering to the particle surface are separated so that the particles are already colloidally wetted in the dispersing chamber. The separated air bubbles coagulate and can escape. This effect contributes to the deaeration of products.

Cleaning in place for the powder paths
In contrast to conventional processes, the powder feed and dispersion are constant and independent of the operator. This ensures reproducibility. Defined processes can also be used to set properties such as droplet and particle size spectrum. In addition to the possibility of integrating the Conti-TDS into existing systems, turnkey systems are used in the smallest of spaces. The possibilities range from fully automatic and recipe-controlled process systems including weighing, control and monitoring. The dispersing unit can also serve as a CIP pump. The powder paths are integrated into the CIP system, as is an additional device that is capable of emptying and cleaning buckets, canisters or hobbocks of any size.

The process systems, which can also be designed for explosion protection, cover a wide performance range. Batches of just one ton can be produced on a version with a capacity of four tons.

ystral Fachartikel Lebensmitteltechnik Dispersionen

Magazine: Food technology
Issue: 04/2023

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