Partic. vol. 11 no. 5 pp. 483-489 (October 2013)
doi: 10.1016/j.partic.2012.10.005

Granulation by spray coating aqueous solution of ammonium sulfate to produce large spherical granules in a fluidized bed

Guanda Wang, Ling Yang, Rui Lan, Tingjie Wang^*, Yong Jin

wangtj@tsinghua.edu.cn

Abstract

Spherical 2–4 mm granules of ammonium sulfate NH₄)₂SO₄ are promising fertilizer for practical use, though only much smaller grains are being produced in industry. This work used coating granulation to produce large spherical granules of NH₄)₂SO₄ in a fluidized bed by spraying its aqueous solution onto 0.9–1.6 mm NH₄)₂SO₄ core particles. However, the overall coating efficiency was only 58% due to loss as dust by attrition of NH₄)₂SO₄ in the vent gas. By adding CaCO₃ or SiO₂ particles into the feed solution, the coating efficiency was increased to over 90%. This increase in coating efficiency was due to a change in the crystallization mechanism of NH₄)₂SO₄. The added CaCO₃ or SiO₂ particles provided a heterogeneous surface that induced NH₄)₂SO₄ to crystallize uniformly to form a more compact structure less susceptible to attrition.

Graphical abstract

Keywords

Ammonium sulfate; Spray coating; Granulation; Fluidized bed; Heterogeneous crystallization