Method for producing urea, apparatus for producing urea, and method for improving existing apparatus for producing urea

An apparatus for producing urea, the apparatus comprising:

• a carbon dioxide separation facility for bringing a carbon dioxide-containing gas into contact with a lean solution, which is an absorbing solution containing low-concentration carbon dioxide, ammonia and water, to absorb and separate carbon dioxide contained in the gas into the lean solution to obtain a rich solution, which is an absorbing solution containing high-concentration carbon dioxide, ammonia and water;
• a rich solution stripping facility for stripping, at a temperature of 100 to 230° C. and a pressure of 1 to 16 MPaG, at least part of the rich solution obtained in the carbon dioxide separation facility to gasify carbon dioxide to separate a gas containing high-concentration carbon dioxide, and to turn the rich solution into an aqueous solution containing low-concentration carbon dioxide and ammonia;
• a high-pressure absorption facility for bringing at least part of the gas separated in the rich solution stripping facility into contact with ammonia at a temperature of 90 to 180° C. and a pressure of 1.0 to 10 MPaG to obtain a carbamate solution;
• and
• a urea synthesis facility for obtaining, at a temperature of 170 to 200° C. and a pressure of 13 to 25 MPaG, a urea synthesis solution using the carbamate solution obtained in the high-pressure absorption facility as part of raw materials.

A method for improving an existing apparatus for producing urea, the method comprising

• adding to the existing apparatus, at least
• a carbon dioxide separation facility to perform a carbon dioxide separation step of bringing a carbon dioxide-containing gas into contact with a lean solution, which is an absorbing solution containing low-concentration carbon dioxide, ammonia and water, to absorb and separate carbon dioxide contained in the gas into the lean solution to obtain a rich solution, which is an absorbing solution containing high-concentration carbon dioxide, ammonia and water, and
• a rich solution stripping facility to perform a rich solution stripping step of stripping, at a temperature of 100 to 230° C. and a pressure of 1 to 16 MPaG, at least part of the rich solution obtained in the carbon dioxide separation step to gasify carbon dioxide to separate a gas containing high-concentration carbon dioxide, and to turn the rich solution into an aqueous solution containing low-concentration carbon dioxide and ammonia
• to enable a method for producing urea, which further includes:
• a high-pressure absorption step of bringing at least part of the gas separated in the rich solution stripping step into contact with ammonia at a temperature of 90 to 180° C. and a pressure of 1.0 to 10 MPaG to obtain a carbamate solution, and
• a urea synthesis step of obtaining, at a temperature of 170 to 200° C. and a pressure of 13 to 25 MPaG, a urea synthesis solution using the carbamate solution obtained in the high-pressure absorption step as part of raw materials.