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Process description
Carbon dioxide and ammonia are converted into urea and water via the formation
of ammonium carbamate at a pressure of about 140 bar. This conversion is
incomplete since the urea formation is an equilibrium reaction, so the urea
solution formed contains unconverted ammonia and carbon dioxide. These components are
recycled at synthesis pressure.
Stripping with CO2 causes the greater part of these components to evaporate from
the solution. Evaporated NH3 and CO2 together with fresh NH3 and
CO2 are condensed in the pool reactor, the heat of condensation being used to produce
LP steam. The condensed NH3 and CO2 are partly converted into urea and water.
In the LP dissociation section, the stripped urea solution is almost entirely freed from the
NH3 and CO2.
The overhead vapors of the reactor are mixed with off-gases of the dissociation section
and then sent to the neutralization section. Here, they are neutralized by means of nitric
acid to form ammonium nitrate. The ammonia present in the urea solution from the urea storage
tank and in the off-gases of the storage tank is also neutralized to ammonium nitrate.
The ammonium nitrate solution and urea solution are then mixed to produce the required UAN solution.
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UREA 
