Ammonia Stripping Processes
In the ammonia stripping process the synthesis section is operated at slightly higher pressure than in CO2 stripping plants, namely at 160 bar and 185-190°C. A molar ratio of 3.2-3.4 is typically maintained in the reactor, achieving a CO2 conversion of up to 62%. The urea-carbamate solution, after leaving the reactor, enters the stripperwhere a large part of the unconverted carbamate is decomposed by the stripping action of the excess ammonia. The residual carbamate and carbon dioxide are recovered downstream of the stripper in two decomposition stages operating at 17 bar (medium pressure) and 3.5 bar (low pressure) respectively. Ammonia and carbon dioxide vapours from the stripper top are mixed with the recovered carbamate solution from the medium-pressure (MP) and low-pressure (LP) sections, condensed in the HP carbamate condenser and recycled to the reactor. The heat of condensation is used to produce LP steam. The urea solution leaving the LP decomposition stage is later concentrated in the evaporation section further downstream.