Patent ID: 6118023
Filing Date: 2000-09-12
Classification: B01D,C07C,Y02P

Abstract:
A method for increasing the capacity of an existing urea process, the existing urea process comprising a process in which ammonia and carbon dioxide are fed to a reactor (R) at an elevated pressure (P), in which a reaction mixture (M1) comprising ammonium carbamate, ammonia, water and urea is prepared, after which, by reducing the pressure once or several times and supplying heat, gaseous ammonia and ammonium carbamate are separated from the reaction mixture in a pressure-reduction section (SC), which reaction mixture results in a liquid mixture (M2) and the gaseous ammonia and ammonium carbamate thus recovered are condensed, in which ammonia (M3') is separated and an aqueous ammoniacal solution of ammonium carbamate (M3) is obtained, which solution (M3) and the ammonia obtained (M3') are reused to prepare urea and in which urea is recovered from the mixture (M2) in a urea-recovery section (U), characterized in that(i) a stripping column (S) is added, in which ammonium carbamate from the reaction mixture (M1) is stripped with carbon dioxide or is thermally stripped at almost the same elevated pressure (P), resulting in a gaseous mixture (G1) and a liquid mixture (M4), which liquid mixture (M4) is fed to the pressure-reduction section (SC),(ii) a condenser (C) is added, which is fed with the gaseous mixture (G1), ammonia and optionally carbon dioxide, in which the gaseous mixture (G1) is condensed at almost the same elevated pressure (P) and at least 30% of the equilibrium amount of urea obtainable under the condensation conditions is furthermore formed, in which a liquid mixture containing urea, water and ammonium carbamate (M5) is formed, which mixture is fed to the bottom of the existing reactor (R), and a gaseous mixture (G2), and(iii) a scrubber (SCR) is added, in which the gaseous mixture (G2) is brought into contact with the aqueous ammoniacal ammonium carbamate solution (M3), in which a liquid (M6) mixture is obtained, which is fed to the condenser (C), and a scrubbed gaseous mixture (G3).