| 摘要 |
<p>In a process for making urea from ammonia and carbon dioxide, the heat of formation of ammonium carbamate is controlled by using a heat-exchanger comprising bundles of cooling elements, each element consisting of two straight concentric pipes constructed so that the coolant is fed to the inner pipe and is discharged through the space between the inner and outer pipes, the coolant being a urea solution obtained by expansion of the hot synthesis urea solution. Using the urea solution as the coolant serves to free the solution of ammonium carbamate, which decomposes to give ammonia and carbon dioxide, and to concentrate the urea solution. It is preferred to use, as coolant, a urea solution from which a substantial portion of the ammonium carbamate has already been removed, e.g. by stripping with carbon dioxide and, subjecting the urea solution to a pressure reduction. The process and apparatus are described by reference to drawings (not shown).</p> |
