Prilled Urea Production from Ammonia (CO2 Stripping Process)

The process under analysis comprises two major sections: (1) Urea Formation; and (2) Urea Treatment, Prilling and Packaging.

Urea Formation. Carbon Dioxide (CO2) is compressed and fed to a stripping column, where unconverted carbamate in the urea solution from reactor downstream is decomposed into ammonia (NH3) and CO2, which are stripped off by the CO2 feed. The urea solution is routed to a Low Pressure (LP) Decomposer downstream, while the off-gas is fed to the Pool Condenser, along with fresh NH3 and recovered carbamate solution from downstream. In this vessel, NH3 and CO2 react forming carbamate. A gas-liquid mixture is directed to a Reactor where urea is generated. An urea solution is routed to CO2 stripping, while a gaseous stream is directed to a High Pressure (HP) Scrubber, where water, unreacted CO2 and NH3 are absorbed in a carbamate solution and conveyed to the Pool Condenser. Non-condensables withdrawn from the HP Scrubber are directed to NH3 Absorbers downstream, where they are washed with process condensate, and the off-gas, virtually free of NH3, is purged.

Urea Treatment, Prilling and Packaging. The urea solution from the CO2 Stripping is fed to the LP Decomposer to remove residual NH3 and CO2, which are then condensed, generating a carbamate solution that is used in the HP Scrubber. The urea solution, virtually free of carbamate, is concentrated in Evaporators, and sent to the Prilling area, while the process condensate is directed to the Condensate Treatment area, where it is treated and can be used in other parts of the plant. Urea melt, from the evaporators, is sprayed from the top of the prilling tower, forming liquid droplets that cool and solidify as they fall forming the urea prills. The prills are conveyed and sent to the Packaging area, where they are packed in bags and stored.