Granulation of powders esp fertilisers - including pregranulation step using water vapour

摘要

Granules are produced from powdered materials by submitting the powder to mechanical movement in a wet medium in two stages:- (1) mixing the powder with a soln. salt in a mixing appts. into which water vapour is injected to give a partial granulation, and (2) transporting the pregranules, accompanied by powdered material, to a drum or plate appts. where granulation is completed. The process is esp. suitable for the prepn. of phosphate fertiliser granules which disintegrate rapidly on contact with wet soil or rain. The sol. salt is pref. NaCl, CaCl2 NH4Cl, (NH4)2SO4, NH4NO3 or urea, and is added to the powdered material in a ratio of at least 2-5%.