Abstract: Process for the preparation of urea from ammonia and carbon dioxide in which a submerged condenser is used as high-pressure carbamate condenser and the urea synthesis solution leaving the submerged condenser is transferred to the reactor by means of an ejector. In particular, this relates to a process in which a pool condenser is used as submerged condenser.

Abstract: Process for the preparation of urea, in which the gas stream which is released during the synthesis of melamine and is composed essentially of ammonia and carbon dioxide is used to synthesize urea, in which process the gas stream which originates from a high-pressure melamine process and is composed essentially of ammonia and carbon dioxide is condensed at a pressure virtually equal to the pressure in the melamine reactor, in which process substantially anhydrous ammonium carbamate is formed, after which said ammonium carbamate is fed to a high-pressure section of a urea stripping plant.

Abstract: Process for the preparation of urea in whicha urea synthesis solution containing carbamate and free ammonia is formed in a high-pressure part in a synthesis zone at an NH.sub.3 /CO.sub.2 molar ratio of up to 4:1, a temperature of at least 175.degree. C.