DRYING AND MIXING IN A VACUUM SHOVEL DRYER

Horizontal Lödige dryer systems guarantee precisely reproducible, consistent and reliable process sequences. All shovel dryer versions can be built in a containment design.

Using the mechanical fluid bed generated during the Lödige mixing process makes the drying process gentle, yet efficient. Intense, homogeneous mixing prevents formation of temperature and moisture gradients in the product and simultaneously increases the contact frequency and therefore the heat exchange of the particles with the heated drum walls. With an added vacuum, the drying process can be performed at low temperatures which are gentle to the product. The high temperature gradient between the product and the heating jacket creates a very effective heat influx. The product moisture removed in the drying process can also be recycled (solvent recovery).

The Laboratory vacuum shovel dryer DRUVATHERM® is a horizontal, batch vacuum dryer with a frequency-controlled mixing unit. This mixer consisting of mixing elements adapted to the process and arranged on a shaft according to a specific system - is installed in a cylindrical mixing drum equipped with a temperature control jacket.

Rotation of the mixing unit generates a three-dimensional product movement in which all of the product is constantly in motion.

The contact frequency of particles with the heat exchange surface (heated wall of the machine) generated by this mechanically generated fluid bed leads to shorter drying times. The chopper rotating at high speeds fitted to the side of the mixing drum is used to chop the product during transition between phases (lumpy/grainy/powdered). Product surfaces are opened up during this process. This leads to a significant increase in drying capacity and prevents moisture and temperature gradients. Fine particles pulled along by solvent vapours are separated in the filter and returned to the product bed through pneumatic filter cleaning.