Process and Plant for the Production of an Aqueous Solution Comprising Urea

A plant for the production of an aqueous solution comprising urea for use in the removal of nitrogen oxides from combustion gas or fumes, the plant comprising a urea synthesis section and a urea recovery section in fluid communication with each other, further comprising:

• a section of washing with carbon dioxide arranged downstream of said urea recovery section,
• a feed duct arranged between said urea recovery section and said washing unit for feeding at least a part of a urea-concentrated aqueous solution comprising residual free ammonia obtained in said urea recovery section to said washing section,
• a feed duct of carbon dioxide to said washing section,
• a duct for the outlet of a urea-concentrated aqueous solution comprising carbamate and essentially lacking in free ammonia from said washing section, and
• a water feed duct in fluid communication with said outlet duct from the washing section, for diluting said urea-concentrated aqueous solution comprising carbamate and essentially lacking in free ammonia until the desired concentration of urea in aqueous solution is reached.

A plant for the production of an aqueous solution comprising urea for use in the removal of nitrogen oxides from combustion gas or fumes, the plant comprising a urea synthesis section, a urea recovery section and an evaporation section comprising a first evaporator and a second evaporator, said sections being in fluid communication with each other, further comprising:

• a washing section with carbon dioxide arranged downstream of said urea recovery section,
• a feed duct arranged between said first evaporator and said washing unit for feeding at least a part of a urea-concentrated aqueous solution comprising residual free ammonia obtained in said first evaporator to said washing section,
• a feed duct of carbon dioxide to said washing section,
• a duct for the outlet of a urea-concentrated aqueous solution comprising carbamate and essentially lacking in free ammonia from said washing section, and
• a water feed duct in fluid communication with said outlet duct from the washing section, for diluting said urea-concentrated aqueous solution comprising carbamate and essentially lacking in free ammonia until the desired concentration of urea in aqueous solution is reached.

A method of modernisation (revamping) of a pre-existing plant for the production of urea from ammonia and carbon dioxide of the type comprising a urea synthesis section and a urea recovery section in fluid communication with each other, comprising the steps of:

• arranging a section of washing with carbon dioxide downstream of said urea recovery section,
• arranging a connection duct between said urea recovery section and said washing section for feeding at least a part of a urea-concentrated aqueous solution comprising residual free ammonia exiting from said urea recovery section to said washing section,
• arranging a feed duct of carbon dioxide to said washing section,
• arranging a duct for the outlet of a urea-concentrated aqueous solution comprising carbamate and essentially lacking free ammonia from said washing section, and
• arranging a water feed duct in fluid communication with said outlet duct for diluting said urea-concentrated aqueous solution comprising carbamate and essentially lacking in free ammonia, until the desired concentration of urea in aqueous solution is reached.

A method of modernisation (revamping) of a pre-existing plant for the production of urea from ammonia and carbon dioxide of the type comprising a urea synthesis section, a urea recovery section and an evaporation section comprising a first evaporator and a second evaporator, said sections being in fluid communication with each other, comprising the steps of:

• arranging a section of washing with carbon dioxide downstream of said urea recovery section,
• arranging a connection duct between said first evaporator and said washing unit for feeding at least a part of a urea-concentrated aqueous solution comprising residual free ammonia obtained in said first evaporator to said washing section,
• arranging a feed duct of carbon dioxide to said washing section,
• arranging a duct for the outlet of a urea-concentrated aqueous solution comprising carbamate and essentially lacking in free ammonia from said washing section, and
• arranging a water feed duct in fluid communication with said outlet duct for diluting said urea-concentrated aqueous solution comprising carbamate and essentially lacking in free ammonia until the desired concentration of urea in aqueous solution is reached.