SEPARATION METHOD FOR UNCONVERTED SUBSTANCE

摘要

PURPOSE:To synthesize urea with high thermal economics, by carrying out separation of unconverted substances from an urea synthesis solution in reaction of NH3 with CO2 by CO$2 stripping under the same pressure as that in synthesis and subsequent heating and depressurizing treatment. CONSTITUTION:NH3 is reacted with CO2 under a given pressure corresponding to the molar ratio of NH3/CO2 and the resultant ureas synthesis solution is stripped in a stripper 5 to separate unconverted substances in a pipe 7. The resultant synthesis solution is depressurized by a pressure reducing valve 9 and heated by heat exchange in a condenser 10 and then fed to a separator 16 to separate the unconverted substances 19. An aqueous solution from the subsequent finishing step of the synthesis solution discharged from a pipe 17 is fed through a pipe 21 into an absorber 20 to absorb a gaseous mixture of the unconverted substances from the separator 16. The formed aqueous solution of the unconverted substances is passed through a washer 25 to the condenser 10 and brought into contact with the unconverted gas mixture from the stripper 5 to form ammonium carbamate. The synthesis solution from the stripper is heated by released heat in the formation.