Improvements relating to the recovery of waste gases in the synthesis of urea from ammonia and carbon dioxide

摘要

In a process for the separation of the components of a mixture of ammonia, carbon dioxide and aqueous vapour by the selective absorption of ammonia in aqueous solutions of ammonium salts of strong acids at superatmospheric pressures, as described in the parent Specification, the absorption temperature is kept constant by circulating the absorbing solution after pressure release on its issue from the absorption column through a heat exchanger in the absorption column. The gaseous mixture is passed from a container 2 into a column 3 where ammonia is absorbed and the solution is released through a valve 11 to a lower pressure and is then passed to a vessel 12 where part of the ammonia distils and thereby the solution is cooled. The solution is then conveyed, wholly or partially, to a heat exchanger 4, where heat evolved by the absorption of the ammonia is removed by the solution. As the solution is heated passing through the heat exchanger 4, ammonia is distilled from it and is separated in a vessel 13, the solution may then be wholly conveyed to a column 8 where remaining ammonia is removed by steam heating, or partially recycled to the exchanger 4. Specification 740,638 also is referred to.