Block diagram of Urea Production from NH3 and CO2

Block Diagram of Urea Production Process, step in urea production
Urea is a primary fertilizer having a rich concentration of Nitrogen when compared to other inorganic chemical fertilizers. Urea is produced in large scale with reference to other NPK fertilizers because of its use in producing various grade fertilizers, as a nitrogen supplement. About 45-47% of nitrogen is present in a unit amount of urea and melts at 132.7-degree centigrade.  Urea chemically called as carbamide when used in the production of synthetic fibres and urea resins.

Below are some of the famous methods and processes that explain how urea can be produced by industrial scale:

  • Sindri method
  • Solvay process
  • Dupont process
  • Krase process
  • Inventa process
  • Chemico process
  • Montecatini process(solution recycle)
  • Pechiney process
  • Stamicarbon process(Dutch State Mines)
  • Allied chemical high-pressure process
  • Toyo Koatsu process

In a snamprogetti method, urea synthesis reactor operates at 350-4000F and 2500-3500 psig to convert NH3 and CO2 to ammonium carbamate. Due to endothermic reaction forward reaction is favoured by increasing temperature and pressure.  The formed ammonium carbamate is dehydrated to give molten urea. Then a series of decomposition and condensation loop will strip out the unreacted ammonia, carbon dioxide and recycle them to again in the process. At the end of the process, stream pressure is let down and fed to vacuum evaporator to concentrate molten urea to 99% pure. A scrubbing and extraction loop of condensate and urea solution is designed to recover the ammonia and carbon dioxide gases that are not reacted. Finally, a superb technique of granular formation of molten urea is done in a prilling tower, it really a nice and interesting unit operation. A bucket rotates and sprays out molten urea through its nozzles. As the sprayed matter travel to the bottom of the prilling tower, they cool down by counterflow of cool dry air forming perfect regular spherical particles of urea.  On observing the beautiful technique in granular operation, helps to learn more about the design of prilling tower. All the condensate is recycled back to the plant with well-engineered condensate loop system. The above block diagram of urea production shows the unit-operation streaming.

The chemical equation for the production of urea fertilizer:

CO2 + 2NH3 → NH2COONH4  (ammonium carbamate)       ∆H= -155KJ/mol

NH2COONH4   NH2CONH2 (urea)+ H2O                                 ∆H=  +4.2Kcal/mole

Chemical formula of urea is NH2CONHand the molecular weight is 60.06 gram/mole.

A brief explanation of block diagram of urea production plant:
Typical blocks in urea production plantUnit process/operationsProcess Description
CO2 compressionCompressor/turbineCompressed to 160 atm
Urea reactorChemical reactorUrea production at 188 oC, 155 kg/cm2
Medium Pressure decomposerIndirect Stripper (separator)Convert carbamate to ammonia and carbon dioxide at 18 atm
Low-pressure decomposerIndirect Stripper(separator)Convert remaining carbamate to NH3 and CO2 at 4.5 atm
Vacuum pre-concentratorVacuum evaporator(separator)Concentration of urea is done by removing water.
Medium pressure absorberAbsorptionAmmonia recovery from carbamate
Prilling towerGranulatorFormation of urea granules from the slurry