| 摘要 |
Process for preparing urea in which, - at a pressure of 125-350 bar and the corresponding temperature, a urea synthesis solution containing carbamate is formed from carbon dioxide and an excess of ammonia, - in a first decomposition step part of the carbamate is decomposed, with supply of heat and in countercurrent contact with a stripping gas, and the resulting gas phase is in part condensed in a first con-densation zone, - in at least two further decomposition steps a further part of the carbamate still present is decomposed and the gas mixture formed is separated off, in the first of the further decomposition steps a pressure of 4-40 bar being maintained, - the remaining urea-containing solution is processed by evaporation to form a concentrated urea solution, the heat required for evaporation being obtained at least in part by condensation of the gas mixture obtained in the first of the further decomposition steps. The gas mixture used in the first evaporation step is formed by the gas phase resulting from the heat exchange between the part of the stripped urea synthesis solution expanded to a pressure of 4-40 bar and the condensing gas mixture in the first condensation zone. |
