| 摘要 |
<p>In a process for the synthesis of urea the improvement is described in which the decomposition and separation of unconverted raw materials which are conventionally performed at a pressure equal to the pressure of the synthesis reaction by stripping and formation of ammonium carbamate, are partially replaced by decomposition and separation thereof and absorption thereof under a medium pressure which is lower than the pressure of synthesis reaction, the unconverted materials being separated as a first gaseous mixture under the synthesis pressure, a second gaseous mixture under a medium pressure which is lower than the pressure of synthesis reaction and a third gaseous mixture under a third pressure which is lower than the said medium pressure, and the separated unconverted materials recycled by absorption of the second gaseous mixture in a solution of the third gaseous mixture at the medium pressure and absorption in the resulting solutions at the synthesis pressure of a portion of the first gaseous mixture, the resulting aqueous solution and unabsorbed first gaseous mixture being recycled to the synthesis section, and in which the heat generated in the said absorption is utilized in the overall process to reduce the amount of high pressure steam required in the overall process and reduce the amount of low pressure steam generated, the ratio of total ammonia to total carbon dioxide in the synthesis section being maintained within the range of from 2.8 to 5.0.</p> |
