Process for producing biuret from urea

A method of modifying a urea plant wherein:

• the urea plant, before modification, comprises at least:
• a high-pressure urea synthesis section;
• a recovery section;
• a low-biuret urea section arranged to convert a urea aqueous solution taken from the recovery section into solid urea, said low-biuret urea section including at least a water removal section to remove water from the solution and obtain a urea melt, and a shaping section to convert the urea melt into solid urea;
• the method includes adding a high-biuret urea section including at least:
• a dedicated water removal section, configured to remove water from a stream of urea aqueous solution and to obtain urea melt;
• said stream of urea aqueous solution containing no more than 100 ppm by weight, preferably no more than 50 ppm by weight, of formaldehyde, more preferably said stream of urea aqueous solution being free of formaldehyde;
• a biuret reactor arranged to process said urea melt under biuret-forming conditions to decompose urea into biuret and ammonia and obtain a biuret-containing urea melt;
• a line arranged to add water or an aqueous stream to said biuret-containing urea melt at a dilution point, obtaining a solution;
• a crystallization section arranged to process said solution obtained after the dilution of the melt and to obtain a slurry including precipitated solid phase and a mother liquor and to process the slurry obtaining a solid phase separated from the liquid phase;
• optionally, a drying section adapted to further remove water from said solid phase for the obtainment of a granular product or a powder;
• the method further comprising the provision of a line arranged to feed a portion of the aqueous solution from the recovery section to the newly installed high-biuret urea section.