FIELD: chemistry.
SUBSTANCE: method of producing urea from ammonia and carbon dioxide involves the following steps: feeding ammonia and carbon dioxide into a urea synthesis section working at given high pressure, reaction of ammonia and carbon dioxide in the synthesis section to obtain aqueous solution containing urea, ammonium carbamate and ammonia, feeding a portion of the said aqueous solution containing urea, ammonium carbamate and ammonia into a processing section working at given average pressure for extraction of ammonium carbamate and ammonia contained therein, dissociation of the said portion of the aqueous solution containing urea, ammonium carbamate and ammonia in the processing section to obtain aqueous solution of urea and a vapour phase containing ammonia, carbon dioxide and water, condensation of said vapour phase containing ammonia, carbon dioxide and water in the processing section to obtain aqueous solution of ammonium carbamate, recirculation of said aqueous solution of ammonium carbamate into the urea synthesis section, feeding the remaining portion of the said aqueous solution containing urea, ammonium carbamate and ammonia into a decomposition apparatus in the urea extraction section through an evaporation zone, essentially working at said given high pressure, and characterised by that it also involves the following steps: feeding aqueous solution of urea obtained after dissociation in the processing section into the decomposition apparatus in the urea extraction section working at given low pressure, decomposition of the aqueous solution of urea in the decomposition apparatus of the urea extraction section to obtain concentrated urea solution and a second vapour phase containing ammonia, carbon dioxide and water, condensation of the second vapour phase in the condenser of the urea extraction section linked with said decomposition apparatus to obtain recycled aqueous solution of ammonium carbamate. The invention also relates to apparatus for realising said method and a method of renovating an already mounted installation.
EFFECT: high conversion of carbon dioxide to obtain urea with low power consumption.
12 cl, 1 dwg
