Problem No. 8: Urea prilling buckets

Prilling buckets are the oldest technology to form solid urea in a urea plant. In the top of a concrete prilling tower a bucket with numerous holes rotates releasing urea melt droplets, which cool and solidify against the rising air. At the bottom of the prilling tower solid urea prills are collected and sent to storage. It is estimated that about 82% of all urea plants worldwide produce prills. Various designs of prilling buckets are available in the market. What are the design criteria for prilling buckets and what are the experiences with the various designs?