Prill

A prill is a small aggregate of a material, most often a dry sphere, formed from a melted liquid. The material to be prilled must be a solid at room temperature and a low viscosity liquid when melted. Prills are formed by allowing drops of the melted prill substance to congeal or freeze in mid-air after being dripped from the top of a tall prilling tower. Fertilizers (ammonium nitrate, urea, NPK fertilizer) and some detergent powders are commonly manufactured as prills.