Application Note — Chemical
Drying Pigment Filter Cake in a Vacuum Rake Dryer
Pigment filter cake, water-wet, paste consistency
Prepared from Ruibo product data and typical operating conditions. It is not a specific customer project.
The Challenge
Pigment filter cake arrives from the filter press as a dense, water-wet paste. Drying it in a tray oven drives surface water off quickly but leaves the cake case-hardened, so the last of the moisture has to diffuse through a crust and the batch takes far longer than the first hour suggests. Colour shift is the other risk: pigment pastes that sit on a hot surface discolour at the contact layer.
The Solution
A ZPG vacuum rake dryer addresses both problems with the same mechanism. The jacket heats the wall, the rake keeps scraping the product back into contact with it, and the vacuum lowers the boiling point so the jacket can run cooler for the same evaporation rate. Continuous renewal of the surface is what prevents the crust from forming in the first place, rather than breaking it up after it has formed.
Project Process
- Charge the wet cake through the top opening and close the vessel; the rake starts turning at low speed
- Apply vacuum and jacket heat together — the boiling point falls, so water leaves at a jacket temperature the pigment tolerates
- Continue until the batch reaches the target moisture, then break vacuum and discharge through the bottom outlet