Solids drying rate question

[hollerg]

Anyone have experience reducing moist product adhesion to a dryer heat transfer surface, using a low friction, thermally conductive coating or finish?

The dryer is continously processing a thick slurry through the paste phase into a powder.

What are the heat transfer ramifications of doing this? Should heat transfer should go up because of less "fouling" rather than down because of the coating? In this case the coating would be a diamond like coating covalently bonded to the heat transfer surface, with a conductivity like graphite.

Background
A thick slurry is dried in a continous dryer. It passes through the paste phase, into a free flowing powder, if low enough in moisture. Too much moisture and the organic salt tends to be cohesive/adhesive to the dryer wall. At higher temperature differential (at higher rates), the agitated dryer loses heat transfer effectiveness. Fouling is reversable if one backs off on rate (resulting in lower wall temperature). The fouling is periodic just below this rapid fouling zone. Lowering the inventory restores the lost heat transfer.

That the fouling clears so easily makes me think that a packed solids layer forms against the cylindrical wall. Lowering the inventory allows material to be sheared off/dislodged by the impeller and gravity. One root cause seems to be the degree of stickiness to the metal, causing a drop in performance.

To reduce adheasion/friction/surface energy of the wall, I was thinking of adding a diamond like coating as it's low friction, and has high thermal conductivity.

 

[MedicineEng]

If the fouling clears easy, why don't you consider to use a vibrator? Time to time it vibrates and the film that is adhered to the walls will fall down.

Hope that helps.

 

[prajithtp]

Using of high efficiancy centrifuge before the drying step is highly effective and can make reduce the moisture content in the API to a considerable amount.