Problem No. 13: 3-Way valves in urea melt lines

In nearly all urea plants, urea and water is separated in an evaporation or concentration section at vacuum pressures. The urea melt can have a concentration of 99.6 wt-% when the urea melt is sent to a prilling tower or a Sandvik Process Rotoformer or a somewhat lower concentration when a granulation technology is applied.

Obviously it is important to control the temperature of the urea melt just above the crystallisation temperature in order to maintain it in liquid condition. On the other hand, when the temperature is too high several negative side reactions in the urea melt occur, resulting in higher biuret contents in the final product and higher ammonia and urea dust emissions from the finishing section.