Dedert roto-flash dryers - high performance drying for cakes, pastes, and semi-solids

Dedert’s roto-flash dryer is a compact and efficient solution designed specifically for drying filter cakes, pastes, and pumpable materials. It is ideal for products that are insoluble or only slightly soluble in water and have no internal binding strength. With decades of experience in thermal separation technologies, Dedert delivers precise control over particle size, moisture content, and throughput, even in the most demanding drying applications.

How it works

The roto-flash dryer is a specially designed agitated drying process where wet feed materials are rapidly disintegrated and dried in a rotating air stream. The vertical drying chamber includes:

A tangential hot air inlet through an annular plenum, which creates a swirling flow of drying gas
A central rotor that mechanically disperses feed material and promotes attrition
A top-mounted outlet with an adjustable orifice that controls particle residence time and allows only properly sized particles to exit the chamber

This mixed flow drying process provides short air residence times, typically less than one second, while maintaining longer product residence time. The result is highly efficient moisture removal and uniform powder quality.

Feeding system design

A stable and consistent feed is critical for optimal dryer performance. Dedert designs robust feed systems tailored to the characteristics of each material:

Standard cakes and pastes are typically fed via screw feeders
Thixotropic or sticky materials may require a twin-screw feeder or pump to ensure proper flow
A feed vat with load cells is used to monitor and control the feed rate precisely

An integrated agitator conditions the feed before drying to ensure even dispersion and to prevent clogging or bridging in the screw.

Powder control and particle size

Final powder properties are controlled by:

Orifice diameter: Smaller openings increase retention time, resulting in finer powders
Rotor speed (RPM): Affects attrition and contributes to particle size control, although changes are usually modest

This allows for production of fine powders with consistent moisture levels and a narrow particle size distribution.

Drying parameters and safety

Dedert’s roto-flash dryers are capable of operating across a wide temperature range, depending on the specific material:

Inlet temperature range	Product types
Low (140–200°C)	Organic pigments, dyestuff intermediates, black iron oxide, thiocarbamates
Medium (200–400°C)	Aluminum hydroxide, copper phthalocyanine, bordeaux mixture, di-calcium phosphate
High (400–750°C)	Titanium dioxide, silica, zeolite, calcium carbonate, kaolin, manganese oxide

The maximum design inlet temperature is 750°C. However, the temperature should be selected below the product's melting point to avoid deposits. It must also stay below the minimum ignition or critical exothermic reaction temperature for safety.

The outlet air temperature will determine the final moisture content of the product.

Advanced design features

Dedert’s roto-flash dryer incorporates advanced mechanical and thermal engineering to ensure high performance, durability, and maintainability in harsh process environments. Key design enhancements include:

Air-cooled bearing block and shaft designed for continuous operation at higher temperatures
Improved shaft-to-bearing block coupling for better torque transmission and stability
Reinforced rotor arrangement for enhanced rigidity and durability
Larger bearings in the bearing block for extended service life
Optimized management of differential thermal expansion in the hot chamber to minimize stress and deformation
Dedicated gearbox maintenance trolley for easier, safer access during servicing
Adapted materials of construction to meet specific chemical or thermal process requirements