Low biuret urea

Claim 1

IN A PROCESS FOR RECOVERING HIGH PURITY UREA CRYSTALS IN WHICH AMMONIA AND CARBON DIOXIDE ARE REACTED IN A REACTION ZONE UNDER UREA SYNTHESIS CONDITIONS TO PRODUCE AN AQUEOUS EFFLUENT CONTAINING UREA OF LOW BIURET CONTENT; SAID EFFLUENT IS TREATED UNDER A REDUCED PRESSURE TO SUBSTANTIALLY COMPLETELY REMOVE AMMONIA AND CARBON DIOXIDE GASES AND A PORTION OF THE WATER FROM SAID EFFLUENT, THEREBY PROVIDING A CONCENTRATED AQUEOUS UREA SOLUTION OF APPRECIABLE BIURET CONTENT; SAID CONCENTRATED AQUEOUS UREA SOLUTION IS PASSED TO A CRYSTALLIZATION ZONE MAINTAINED UNDER CONDITIONS TO PRODUCE HIGH PURITY UREA CRYSTALS FROM A UREA-CONTAINING CRYSTALLIZATION MOTHER LIQUOR WHICH IS THEREBY ENRICHED TO BIURET, THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY WITHDRAWING A PORTION OF SAID CRYSTALS AND SAID BIURET-ENRICHED UREA-CONTAINING LIQUOR FROM SAID CRYSTALLIZATION ZONE, SEPARATING SAID LIQUOR FROM SAID CRYSTALS, PASSING A MAJOR PORTION OF SAID LIQUOR BACK TO SAID CRYSTALLIZATION ZONE TO CONTROL THE RATIO OF MOTHER LIQUOR TO CRYSTALS OF UREA IN SAID CRYSTALLIZATION ZONE PASSING THE REMAINING PORTION OF SAID LIQUOR TO SAID REACTION ZONE TO CONVERT THE BIURET CONTENT THEREOF TO UREA AND TO RECOVER THE UREA CONTENT OF THE LIQUOR.