Process for preparing urea

Claim 1

In a process for synthesizing urea by reacting carbon dioxide and ammonia at a pressure of 80-200 atm. and a temperature of 170°-190° C. in a urea synthesis zone, heating the thus-produced urea synthesis solution and contacting said solution with a stripping gas, thereby forming a gaseous mixture composed primarily of ammonia, carbon dioxide and water vapor, and recirculating said gaseous mixture, said heating and contacting being effected at substantially the same pressure as that maintained in the urea synthesis zone, the improvement comprising: a. in a first step, increasing the temperature of said urea synthesis solution by said heating to a temperature of 205°-250° C. in a heat exchange zone thereby liberating a mixture of gases prior to contact with said stripping gas, and b. in a second step, effecting said contacting of the heated synthesis solution of the first step (a) with said stripping gas under substantially adiabatic conditions, thereby removing and expelling the unconverted reactants with said stripping gas.