Urea production process and plant

A process for the preparation of urea granules comprising the steps of:

• a) reacting ammonia and carbon dioxide at urea synthesis pressure to obtain a urea-containing effluent and processing said effluent in at least one recovery step at a lower pressure obtaining an aqueous urea solution;
• b) subjecting the aqueous urea solution to an evaporation step wherein water is removed from said aqueous urea solution so as to obtain a urea melt and an aqueous vapour phase;
• c) subjecting said urea melt to granulation in presence of fluidising air obtaining solid urea granules and a granulation offgas containing air and urea dust;
• d) conveying the granulation offgas to a scrubbing step performed with an aqueous scrubbing agent to remove urea dust from the offgas and to produce an aqueous urea solution containing urea removed from the offgas and a purified gaseous stream;
• e) contacting a first portion of the aqueous urea solution of step (d) with water to yield said aqueous scrubbing agent, and recirculating said aqueous scrubbing agent to the scrubbing step;
• f) feeding a second portion of said aqueous urea solution of step (d) to an evaporation step wherein said evaporation step is conducted in presence of an air stream to yield a recovered urea solution and a water-saturated air stream and wherein said evaporation step is conducted at atmospheric pressure or below atmospheric pressure;
• g) recirculating the recovered urea solution obtained at step (f) to the granulation step so that said recovered urea solution is subject to granulation together with the urea melt;
• h) recirculating the water-saturated air stream to step (d) without passing through a condensation step, so that said water-saturated air stream is subjected to a scrubbing step together with the granulation offgas of step (c).