how does a rotary drum dryer work?

Question

how does a rotary drum dryer work, does it invove the passage of dry air??? what is its heating medium

Answer 1

There are many types of drum dryers ....

I am familar with a rotary vacuum dryer used in the waste water industry to dewater sludge. The drum is a fine screen which is partially submerged in the slurry. A vacuum pump draws liquid through the screen with the solids getting trapped on the outside.

The drum has som internal baffles to port the vacuum so only a wedge shapped section of the drum is under a vacuum. This allows the vacuum to draw mainly liquid from the submerged section and to pull air through a smaller section above the water line. This allows air to be drawin through the solids as they rise out of the liquid further drying the material.

as the drum continues to rotate a scrapper blade knocks off the solids and they drop in to a collection area. The scrapped drum section continues to rotate under the liquid surface where the ported vacuum draws in liquid trapping the solids on teh out side and the whole process starts over.