A mixture of compressed CO2 and ammonia under 240 bar (g) pressure is reacted to form ammonium carbamate. This is an exothermic reaction, and heat is absorbed by a boiler to produce steam. The first reactor achieves 78% conversion of the carbon dioxide to urea and the liquid is then furthurly purified. Then, the second reactor receives the gas from the first reactor and recycles the solution. Conversion of carbon dioxide to urea is approximately 60% at a pressure of 50 bar (g). The solution is then purified in the same process as was used for the liquid from the first reactor.
Step 2 - Purification
The major impurities in the mixture at this stage are water from the urea production reaction and unconsumed reactants (ammonia, …show more content…
By the time the mixture is at -0.35 bar (g); solutions of urea dissolved in water and free of other impurities remains. At each stage the unconsumed reactants are absorbed into a water solution which is recycled to the secondary reactor. The excess ammonia is purified and used as feedstock and returned to the primary …show more content…
3) Carbon dioxide stripper
The used UCARSOL is sent to the carbon dioxide stripper. Here the UCARSOL is heated to remove a mixture of CO2 and water, then cooled and reused. The water is then removed from the CO2 by condensation and pure CO2 is sent directly to the urea plant for compression and use in urea synthesis.
4) Ammonia recovery
Gases purged from the ammonia synthesis loop and gases collected during ammonia decompression are mixed and sent to the ammonia recovery system. Here the gas mixture is introduced at the bottom of a column and passed up through a counter-current of cold water. 96% of the ammonia in the gas is absorbed by the water, leaving a gas mixture that is used as a fuel gas to heat the primary reformer. The ammonia is distilled out of the ammonia-water mixture, condensed and then pumped to join the rest of the ammonia from the ammonia synthesizer.
1) Heat recovery
The heat of the reaction in which ammonium carbamate produces steam at 7 brag. This is used in the decomposition and evaporation sections for