Urea is formed in the liquid phase following different reactions, in one of 3 types of process : Once Through ; Partial Recycle ; Total Recycle.
Liquid NH3 is mixed with CO2 gas and any recycled Carbamate under high pressure (3200 psi ), with a conversion of say 60%. Urea solution is then fed through expansion valves and decomposers where unconverted Carbamate is driven off as NH3 and CO2 (and recycled). This produces 78% Urea solution which is concentrated to 99.7% purity in a steam Evaporator and the resultant concentrated solution goes to the Prilling Tower.
Urea is entrained from the Evaporator by the exiting steam, which can contain up to 7,000 mg/m3 with an average size of 3 microns.
Intermediate solution, & thus final product loss
Note: In case of long shutdown periods, fibre should be washed with water to prevent damage.