Urea synthesis apparatus, urea synthesis method, and method for improving existing urea synthesis apparatus

A method for improving an existing urea synthesis apparatus, which includes a urea synthesis reactor, the improving method comprising:

• adding to the existing urea synthesis apparatus at least a first urea synthesis reactor (R1) and means (E) for supplying a first urea synthesis liquid;
• and
• when the existing urea synthesis apparatus does not include a condenser (C) and/or a stripper (S), adding the condenser (C) and/or the stripper (S),
• wherein the condenser (C) is a device including a tube (Ct) inside and for condensing a mixed gas separated in the stripper (S) into an absorbing medium to obtain a condensed liquid by allowing a process fluid containing the absorbing medium and the mixed gas to pass through the tube (Ct) and cooling the process fluid with a cooling medium passing through a shell (Cs) side, the condenser (C) being a device separated from the first urea synthesis reactor (R1) and a second urea synthesis reactor (R2),
• wherein the first urea synthesis reactor (R1) is a device for reacting at least part of components in the condensed liquid obtained in the condenser (C) to obtain the first urea synthesis liquid containing urea, unreacted ammonia, unreacted carbon dioxide, and water, and in the first urea synthesis reactor (R1), a temperature for urea synthesis is 160 to 200° C. a pressure for urea synthesis is 13 to 25 MPa, and N/C is 2.5 to 4.0,
• wherein the means (E) for supplying the first urea synthesis liquid is means for supplying the first urea synthesis liquid obtained in the first urea synthesis reactor (R1) to the second urea synthesis reactor (R2),
• wherein the second urea synthesis reactor (R2) is at least part of the urea synthesis reactor included in the existing urea synthesis apparatus and is a device for reacting at least some components in the first urea synthesis liquid obtained in the first urea synthesis reactor (R1), at least part of raw material ammonia, and at least part of raw material carbon dioxide to obtain a second urea synthesis liquid containing urea, unreacted ammonia, unreacted carbon dioxide, and water, and in the second urea synthesis reactor (R2), a temperature for urea synthesis is 170 to 210° C., a pressure for urea synthesis is 13 to 25 MPa, and N/C is 3 to 4.5, and
• wherein the stripper (S) is a device for stripping the second urea synthesis liquid obtained in the second urea synthesis reactor (R2) using at least part of the raw material carbon dioxide to separate the mixed gas containing unreacted ammonia and unreacted carbon dioxide from the second urea synthesis liquid.