| 摘要 |
<p>Process for concentrating a urea solution by evaporation of water from the urea solution, in which first - in a synthesis zone a urea synthesis solution containing carbamate and free ammonia is formed from carbon dioxide and an excess of ammonia, - in a first decomposition step, at synthesis pressure or lower pressure, a portion of the carbamate is decomposed, - in a further decomposition step, at a pressure between 4 and 40 bar, a further portion of the carbamate still present is decomposed, - the urea solution eventually obtained is concentrated by evaporation in at least two steps, in the first step use being made of the heat released upon condensation of the gas mixture obtained in the decomposition step operated at between 4 and 40 bar. The pressure in the decomposition step operated at between 4 and 40 bar is set at the minimum value at which, with virtually complete condensation of the gas mixture, the amount of heat released is sufficient for reaching the desired final concentration and temperature of the urea solution in the first evaporation step.</p> |
