To produce free flowing particles for further processing; often after powder synthesis and before forming of products, may need to add binder/ wetting agent to keep small particles together, (but not to form hard agglomerate), semi-dry granule.
Sometimes referred as “pelletizing” process; e.g. pressing, extrusion, spray granulation etc.
used to produce alumina, ferrite, clays, tile bodies, porcelain bodies, conventional refractory compositions, catalyst support, and feed materials for glass or metal refining;
Granules may not be spherical, could be cylindrical;
Spray granulation: spray (may contain binder) and stir to make pellets
Formation of Granule Che5700 陶瓷粉末處理 Can be viewed as nucleation & growth process; At first, binder solution droplet touch particle nucleus; capillary force and binder flocculation provide strength
Growth by layering through contact and adhesion; or by nuclei agglomeration;
Rubbing between granules make granules surface smooth
Spray granulation uniformity closely related to liquid content; Hardness: mostly related to binder (and particle characteristics)
Foam index: bubbles in slurry low quality of granules, use foam index to represent bubbles in slurry: foam index (%) = [ T – E ] 100/ T ; T , E = theoretical and experimental density of slurry (the latter contain bubbles)
If necessary, add anti-foam agent;
wall deposit problem
two-fluid nozzle: to lower pressure drop and to get smaller particles
Mass and heat transfer during drying, relative rate may get dry surface with some internal liquid
Wish to separate different particles according to its size, utilize the difference between differently sized particles: e.g. size (sieve opening), motion trajectory; (hydro-cyclone), or forces related to motion; gravity, drag, centrifuge ); density, shape or even surface characteristics;
Sometimes: feed is separated into two streams (not many streams).
Taken from TA Ring, 1996; can add some baffles, to separate large particles