A method for producing urea prills by passing molten droplets of substantially water free urea downwardly through a cooling zone countercurrent to a cooling gas. A dispersion of crystalline particles is maintained in at least a portion of the cooling zone, the crystalline particles having average dimensions of between 2 and 10 microns and being dispersed in the cooling gas in a quantity of between about 8 and 25 mg per m3 of the cooling gas at ambient temperature and pressure, whereby urea prills, built up of relatively small crystallites with random orientation having improved impact strength are formed.

This patent describes the Stamicarbon seeding technology, which increases the impact strength of prills.

1983 Willems Unie van Kunstmestfabrieken 4390483 Method for making urea prills.p