PROCESS AND PLANT FOR SYNTHESIS OF UREA AND MELAMINE Russian patent published in 2018 - IPC C07C273/12 C07D251/60 

FIELD: technological processes.

SUBSTANCE: invention relates to an integrated process for the synthesis of urea and melamine. Process includes: performing a synthesis of urea from ammonia and carbon dioxide using a stripping process, said stripping process comprising at least the steps of reacting ammonia and carbon dioxide in reaction section (5) to form aqueous solution (9) containing urea, ammonium carbamate and unconverted ammonia, and purifying said solution (9) in stripping section (6) to obtain urea solution (10) and gas phase (11) containing ammonia and carbon dioxide, and also includes a condensation step in condensation section (7) wherein at least portion (16) of the synthesised urea is used to produce melamine (18) in a tied-in melamine synthesis plant, also producing off-gas stream (19) from the melamine synthesis process that contains ammonia and carbon dioxide, and said off-gas stream (19) from the melamine synthesis process is recycled to said urea synthesis process either in a gaseous state or after condensation – in liquid state. At least portion (13) of said gas phase (11) obtained from the stripping process is fed directly to said reaction section (5) in a gaseous state. Said urea solution (10) exiting the stripping section is further treated in at least one extraction section (8) to obtain liquid carbamate solution (15) and more concentrated solution (14), and at least a portion of said concentrated solution (14) is used to produce melamine. Off-gases from the melamine synthesis process are recycled to the urea synthesis process by: mixing said off-gas stream (19) from the melamine synthesis process with portion (12) of said gas phase (11) from stripping treatment and at least a portion of said carbamate liquid solution (15) coming from said extraction section (8), thereby obtaining mixed gas and liquid stream (20) condensing said mixed stream (20) in said condensation section (7) to form condensate (22), and feeding said condensate to said reaction section (5). Plant for synthesis of urea and melamine and a modification of the urea synthesis plant are also provided.

EFFECT: invention reduces power consumption.

13 cl, 2 dwg