| 摘要 |
A process for the preparation of urea in which a carbamate- and free ammonia-containing urea synthesis solution is formed from carbon dioxide and excess ammonia in a synthesis zone at a pressure of 125-350 bar, at least a portion of the carbamate present in the urea synthesis solution is decomposed in a stripping zone at the pressure of the synthesis zone or at lower pressure by heat supply and countercurrent contact with a stripping gas, the carbamate decomposition products, together with a portion of the excess ammonia and the stripping gas, are removed from the stripping zone as a gas mixture, at least a portion of the gas mixture obtained is condensed in a condensation zone and the stripped urea synthesis solution is processed into a urea solution or solid urea. The process is characterized in that in the condensation zone also at least 30% of the equilibrium amount of urea achievable under the reaction conditions is allowed to form and the carbamate- and urea-containing mixture is supplied to the synthesis zone. By preference, urea formation is continued until 50-80 %, of the way to the equilibrium has been covered. |
