Process for the manufacture of urea in granular form

Claim 1

A PROCESS FOR THE MANUFACTURE OF SUBSTANTIALLY DRY FREE-FLOWING GRANULES OF UREA CONTAINING LESS THAN 1% OF BIURET BY WEIGHT FROM AN AQUEOUS UREA SYNTHESIS EFFLUENT SUBSTANTIALLY FREE OF UNCONVERTED AMMONIA AND CARBON DIOXIDE: CONSISTING ESSENTIALLY OF PASSING SAID AQUEOUS UREA EFFLUENT THROUGH AN EVAPORATIVE HEATING ZONE, INTRODUCING GASEOUS AMMONIA INTO SAID HEATING ZONE, RAPIDLY HEATING SAID AQUEOUS UREA EFFLUENT DURING ITS PASSAGE THROUGH SAID ZONE AND IN THE PRESENCE OF SAID GASEOUS AMMONIA AT A TEMPERATURE BELOW ABOUT 180* C. AND FOR A TIME SUFFICIENT TO FORM A CONCENTRATED UREA EFFLUENT CONTAINING AT LEAST 97% UREA BY WEIGHT, IMMEDIATELY THEREAFTER PASSING SAID CONCENTRATED UREA EFFLUENT THROUGH A COOLING ZONE WHEREIN SAID EFFLUENT IS COOLED TO A TEMPERATURE WITHIN A FEW DEGREE ABOVE ITS CRYSTALLIZATION TEMPERATURE, IMMEDIATELY THEREAFTER COMMIXING SAID COOLED CONCENTRATED UREA EFFLUENT WITH COOL SOLID UREA FINES WHEREBY SAID COOLED EFFLUENT IS RAPIDLY COOLED TO BELOW ITS CRYSTALLIZATION TEMPERATURE AND ADDITIONAL WATER IS EVAPORATED BY THE HEAT OF CRYSTALLIZATION, AND INTIMATELY MIXING SAILD MIXTURE UNTIL GRANULATION THEREOF TO FORM THE DRY FREE-FLOWING SOLID UREA GRANULES CONTAINING LESS THAN 1% OF BIURET AND LESS THAN 1% OF WATER BY WEIGHT.