Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 88.4.4 Isobaric double recycling process (IDR)DescriptionIn this process, the urea synthesis takes place at 180 – 200 bar and 185 – 190 °C. The NH 3 :CO 2ratio is approximately 3.5 – 4, giving approximately 70 % CO 2 conversion per pass.Most of the unconverted materials in the effluent from the reactor bottom are separated byheating and stripping in two consecutive strippers operated at reactor pressure and heated by25 bar steam. Carbamate is decomposed in the first stripper, with the remaining NH 3 beingremoved in the second stripper using CO 2 as the stripping agent. The overheads from the firststripper are fed directly to the reactor with the overheads from the second stripper beingrecycled to the reactor through the carbamate condenser. The heat of condensation is recoveredas 7 bar steam and used further on in the process.Whereas all the carbon dioxide is fed to the plant through the second stripper, only 40 % of theammonia is fed to the carbamate condenser. The remainder goes directly to the reactor tocontrol the temperature. The ammonia-rich vapours from the first stripper are fed directly to theurea reactor. The carbon dioxide-rich vapours from the second stripper are recycled to thereactor via the carbamate condenser, irrigated with carbamate solution recycled from themedium pressure section of the plant.The heat of condensation is recovered as 7 bar steam which is used downstream in the process.Urea solution leaving the IDR loop contains unconverted ammonia, carbon dioxide andcarbamate. These residuals are decomposed and vaporised in three successive distillers andheated with medium pressure steam and low pressure recovered steam. After this, the vapoursare condensed to carbamate solution and recycled back into the synthesis loop. The ureasolution leaving the LP decomposition for further concentration is fed to two vacuumevaporators in series, producing the urea melt for prilling and granulation.Achieved environmental benefits• enables almost complete raw material recovery• energy savings in comparison with conventional processes.Cross-media effectsNone believed likely in comparison with other urea production processes.Operational dataSee description.ApplicabilityGenerally applicable.EconomicsNo information provided.Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 343