A prill is a small aggregate or globule of a material, most often a dry sphere, formed from a melted liquid through spray crystallization.[1] Prilled is a term used in mining and manufacturing to refer to a product that has been pelletized. ANFO explosive typically comprises ammonium nitrate prills mixed with #2 fuel oil.[2] The pellets are a neater, simpler form for handling, with reduced dust.
The material to be prilled must be in a solid state 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. Certain agrochemicals such as urea are often supplied in prilled form. Fertilizers (ammonium nitrate, urea, NPK fertilizer) and some detergent powders are commonly manufactured as prills.[3] However prilling of ammonium nitrate and urea has in recent years been replaced by fluid bed granulation as this gives strong and more abrasion-resistant granules.[1]
Melted material may also be atomized and then allowed to form smaller prills that are useful in cosmetics, food, and animal feed.