METHOD OF SYNTHESIS OF UREA FROM AMMONIA AND CARBON DIOXIDE Russian patent published in 1995 - IPC

FIELD: chemical technology. SUBSTANCE: urea is synthesized at the molar ratio of ammonia carbon dioxide (2.5-5):1, at 175-220 and under pressure 12-23 MPa at the zone synthesis. Urea solution from reactor is fed to the first stage of thermic decomposition of ammonium carbamide under pressure equal value of pressure synthesis at 200-210 C at external heat input to the decomposition reactor. Waste urea solution is stripped in tower working at adiabatic regime at countercurrent feeding above 70% fresh carbon dioxide of its total quantity feeding for synthesis under pressure by 1-7 MPa lower that at the synthesis stage. Exhausting vapor-gas flow is mixed with carbamate solution in recirculating system obtained at the first stage by condensation of product decomposition. Then mixture is condensed for a few successive condensation stages. Condensation heat is transformed to the urea solution at the stages of its thermic treatment and urea concentration. Stripped urea solution containing ammonia and carbon dioxide at the molar ratio (2-4):1 is decomposed at some, preferably two stages of carbamate decomposition at the average (1-4 MPa) and low (0.35-0.5 MPa) pressure. At the stage of urea concentration under vacuum at 30-100 KPa in interpipe space of heat-exchanger at film regime the mixture of gaseous decomposition products of ammonium carbamate is condensed with recyclizing condensate and fresh ammonia at the ratio ammonia and carbon dioxide nearing to the azeotropic point at which condensation temperature is maximal. Condensation heat is utilized for urea evaporation in the pipe space up to the concentration 88-95% EFFECT: improved method of urea synthesis. 9 cl, 1 dwg