Abstract: The plant is provided with a first rotary reactor where the balls of urea cyanurate are formed and a second reactor where the pyrolysis takes place. The first reactor is provided with an internal helical fin and the second reactor is also rotary. At the exit thereof there is a communication tube placing it in communication with a solids separator vessel which receives an aqueous solution capable of reaching a working level, below which there is the access port of the tube to the vessel. The vessel is provided with a lower drain valve and an upper gas exhaust tube.