Urea is used in several applications like
- Nitrogen fertilizer
- Base chemical in resin, paint and glue production
- Up-stream product of hydrazine, melamine and amidosulfonic aci
- Animal feed and
Some applications of urea need addition of other ingredients in order to provide a more useful product. Therefore the urea granules from the urea production process need to be molten and mixed with other materials. Temperatures of about 130°C support Biuret creation by the combination of two urea molecules and the formation of one ammonia molecule. The Biuret concentration of the final product should be low because Biuret impairs plant growth. Therefore the residence time under elevated temperature must be as short as possible.
Melting and mixing are tasks which can be done very effectively in a horizontal thin film dryer.
In contradiction to a drying process the feed is dry and solid and the product is liquid. There is nearly no evaporation of the feed material and hence no vapour condensation. The urea granules are fed into the dryer and molten by indirect heating. Due to the short residence time Biuret generation is minimal. Additional solid components can be added through a separate nozzle. Liquid components can be injected through the rotor of the dryer. The inlet components are mixed during their way through the dryer to the final product. Looking at urea melting near the inlet of the dryer shows that horizontal thin film dryers are even able to realize high heat transfer rates to solid products. This opens another range of applications like melting of solids and cooling of solid products from drying processes.