Abstract: In the process for urea synthesis, an effluent from a reactor 2 containing urea, ammonium carbamate, excess ammonia and water is introduced in a first heater 3 to separate excess ammonia and to decompose ammonium carbamate, thereby separating them from the liquid phase; then the liquid effluent from the first heater 3 is introduced in a second heater 6 to separate the remaining excess ammonia and to decompose ammonium carbamate in the presence of starting carbon dioxide used as stripping gas, thereby separating them from the liquid phase; the liquid effluent from the second heater 6 is introduced into a urea solution purification step in which pressure is lower than in the above step; and the separated gaseous effluents from the first and the second heaters are returned into the reactor.

Abstract: In a urea synthesis process, the reaction product from the reaction vessel is flowed in series through high pressure, medium pressure and low pressure decomposing and stripping devices to decompose ammonium carbamate to NH.sub.3 gas, CO.sub.2 gas and water vapor, and to remove those gases and unreacted starting materials from the aqueous urea solution. CO.sub.2 gas is used as the stripping gas in the decomposing and stripping devices.

Abstract: The tail gas from the urea synthesis plant is rendered non-explosive by adding thereto a purge gas that is obtained from the ammonia synthesis plant that is usually installed closed to the urea synthesis plant and used for synthesis of ammonia used as starting material for the urea synthesis.